diff --git a/app/models/journable/with_historic_attributes.rb b/app/models/journable/with_historic_attributes.rb
index 088fad697f2e..48b190518e31 100644
--- a/app/models/journable/with_historic_attributes.rb
+++ b/app/models/journable/with_historic_attributes.rb
@@ -264,6 +264,7 @@ def changes_at_timestamp(timestamp)
 
     merge_target_versions_changes!(changes, historic_journable)
     merge_observed_in_versions_changes!(changes, historic_journable)
+    merge_labels_changes!(changes, historic_journable)
 
     changes
   end
@@ -276,12 +277,12 @@ def merge_target_versions_changes!(changes, historic_journable)
   end
 
   def target_versions_changes(historic_journable)
-    old_ids = sorted_version_ids(historic_journable, :target_versions)
-    new_ids = sorted_version_ids(__getobj__, :target_versions)
+    old_ids = sorted_association_ids(historic_journable, :target_versions)
+    new_ids = sorted_association_ids(__getobj__, :target_versions)
 
     {}.tap do |changes|
       changes["version_id"] = [old_ids.first, new_ids.first] if old_ids.first != new_ids.first
-      changes["target_versions"] = [old_ids, new_ids].map { joined_version_ids(it) } if old_ids != new_ids
+      changes["target_versions"] = [old_ids, new_ids].map { joined_ids(it) } if old_ids != new_ids
     end
   end
 
@@ -292,19 +293,34 @@ def merge_observed_in_versions_changes!(changes, historic_journable)
   end
 
   def observed_in_versions_changes(historic_journable)
-    old_ids = sorted_version_ids(historic_journable, :observed_in_versions)
-    new_ids = sorted_version_ids(__getobj__, :observed_in_versions)
+    old_ids = sorted_association_ids(historic_journable, :observed_in_versions)
+    new_ids = sorted_association_ids(__getobj__, :observed_in_versions)
 
     {}.tap do |changes|
-      changes["observed_in_versions"] = [old_ids, new_ids].map { joined_version_ids(it) } if old_ids != new_ids
+      changes["observed_in_versions"] = [old_ids, new_ids].map { joined_ids(it) } if old_ids != new_ids
     end
   end
 
-  def sorted_version_ids(work_package, association)
+  def merge_labels_changes!(changes, historic_journable)
+    return unless __getobj__.respond_to?(:labels)
+
+    changes.merge!(labels_changes(historic_journable))
+  end
+
+  def labels_changes(historic_journable)
+    old_ids = sorted_association_ids(historic_journable, :labels)
+    new_ids = sorted_association_ids(__getobj__, :labels)
+
+    {}.tap do |changes|
+      changes["labels"] = [old_ids, new_ids].map { joined_ids(it) } if old_ids != new_ids
+    end
+  end
+
+  def sorted_association_ids(work_package, association)
     work_package.public_send(association).map(&:id).sort
   end
 
-  def joined_version_ids(ids)
+  def joined_ids(ids)
     ids.join(",").presence
   end
 
diff --git a/app/models/journable/with_historic_attributes/loader.rb b/app/models/journable/with_historic_attributes/loader.rb
index 67c527051971..fa0d474a3259 100644
--- a/app/models/journable/with_historic_attributes/loader.rb
+++ b/app/models/journable/with_historic_attributes/loader.rb
@@ -69,6 +69,7 @@ def load_journal_associations(journalized = journables)
       load_custom_value_associations(journalized, journal_ids)
       load_versions_associations(journalized, journal_ids, kind: "target", association: :target_versions)
       load_versions_associations(journalized, journal_ids, kind: "observed_in", association: :observed_in_versions)
+      load_labels_association(journalized, journal_ids)
 
       journalized
     end
@@ -91,7 +92,20 @@ def load_versions_associations(journalized, journal_ids, kind:, association:)
 
       journalized.each do |work_package|
         version_journals = Array(version_journals_by_journal_id[work_package.journal_id])
-        set_versions_association_from_journal!(work_package:, version_journals:, association:)
+        historic_versions = version_journals.filter_map(&:version).sort_by(&:id)
+        set_association_from_journal!(work_package:, records: historic_versions, association:)
+      end
+    end
+
+    def load_labels_association(journalized, journal_ids)
+      return unless journalized_class.method_defined?(:labels)
+
+      label_journals_by_journal_id = load_label_journals_by_journal_id(journal_ids)
+
+      journalized.each do |work_package|
+        label_journals = Array(label_journals_by_journal_id[work_package.journal_id])
+        historic_labels = label_journals.filter_map(&:label).sort_by(&:id)
+        set_association_from_journal!(work_package:, records: historic_labels, association: :labels)
       end
     end
 
@@ -144,6 +158,13 @@ def load_version_journals_by_journal_id(journal_ids, kind:)
         .group_by(&:journal_id)
     end
 
+    def load_label_journals_by_journal_id(journal_ids)
+      Journal::LabelJournal
+        .where(journal_id: journal_ids)
+        .includes(:label)
+        .group_by(&:journal_id)
+    end
+
     def set_custom_value_association_from_journal!(work_package:, customizable_journals:)
       # Build the associated customizable_journals as custom values, this way the historic work packages
       # will behave just as the normal ones. Additionally set the reverse customized association
@@ -156,11 +177,9 @@ def set_custom_value_association_from_journal!(work_package:, customizable_journ
       work_package.association(:custom_values).target = historic_custom_values
     end
 
-    def set_versions_association_from_journal!(work_package:, version_journals:, association:)
-      historic_versions = version_journals.filter_map(&:version).sort_by(&:id)
-
+    def set_association_from_journal!(work_package:, records:, association:)
       work_package.association(association).loaded!
-      work_package.association(association).target = historic_versions
+      work_package.association(association).target = records
     end
 
     attr_accessor :journables
diff --git a/app/models/journal.rb b/app/models/journal.rb
index 0e7f516832e3..73a5992ec1b8 100644
--- a/app/models/journal.rb
+++ b/app/models/journal.rb
@@ -57,6 +57,7 @@ class Journal < ApplicationRecord
   register_journal_formatter OpenProject::JournalFormatter::Diff
   register_journal_formatter OpenProject::JournalFormatter::FileLink
   register_journal_formatter OpenProject::JournalFormatter::IgnoreNonWorkingDays
+  register_journal_formatter OpenProject::JournalFormatter::Labels
   register_journal_formatter OpenProject::JournalFormatter::MeetingStartTime
   register_journal_formatter OpenProject::JournalFormatter::MeetingState
   register_journal_formatter OpenProject::JournalFormatter::MeetingWorkPackageId
@@ -133,6 +134,7 @@ class Journal < ApplicationRecord
   has_many :custom_comment_journals, class_name: "Journal::CustomCommentJournal", dependent: :delete_all
   has_many :project_phase_journals, class_name: "Journal::ProjectPhaseJournal", dependent: :delete_all
   has_many :storable_journals, class_name: "Journal::StorableJournal", dependent: :delete_all
+  has_many :label_journals, class_name: "Journal::LabelJournal", dependent: :delete_all
   has_many :work_package_version_journals, class_name: "Journal::WorkPackageVersionJournal", dependent: :delete_all
   # Row lifecycle is owned by work_package_version_journals above.
   # rubocop:disable Rails/HasManyOrHasOneDependent
diff --git a/app/models/journal/label_journal.rb b/app/models/journal/label_journal.rb
new file mode 100644
index 000000000000..f83523b30bb7
--- /dev/null
+++ b/app/models/journal/label_journal.rb
@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+class Journal::LabelJournal < Journal::AssociatedJournal
+  self.table_name = "label_journals"
+
+  belongs_to :label
+end
diff --git a/app/models/work_package/journalized.rb b/app/models/work_package/journalized.rb
index 99d7b0e4ccf3..86ffc7a71554 100644
--- a/app/models/work_package/journalized.rb
+++ b/app/models/work_package/journalized.rb
@@ -107,6 +107,7 @@ def self.event_url
     register_journal_formatted_fields "project_phase_definition_id", formatter_key: :project_phase_definition
     register_journal_formatted_fields "target_versions", formatter_key: :target_versions
     register_journal_formatted_fields "observed_in_versions", formatter_key: :observed_in_versions
+    register_journal_formatted_fields "labels", formatter_key: :labels
 
     # Joined
     register_journal_formatted_fields :parent_id, :project_id,
diff --git a/app/services/journals/create_service/association.rb b/app/services/journals/create_service/association.rb
index 60c431eabafd..a3c7fab0e141 100644
--- a/app/services/journals/create_service/association.rb
+++ b/app/services/journals/create_service/association.rb
@@ -34,7 +34,7 @@ class Association
 
     # Core associations are defined here. Module-specific associations can be defined in engines
     # using `Journals::CreateService::Association.register`.
-    @registry = Set.new(%i[Attachable CustomComment Customizable ProjectPhase WorkPackageVersion])
+    @registry = Set.new(%i[Attachable CustomComment Customizable Labelable ProjectPhase WorkPackageVersion])
 
     class << self
       def register(*names)
diff --git a/app/services/journals/create_service/labelable.rb b/app/services/journals/create_service/labelable.rb
new file mode 100644
index 000000000000..60fa1e70badb
--- /dev/null
+++ b/app/services/journals/create_service/labelable.rb
@@ -0,0 +1,86 @@
+# frozen_string_literal: true
+
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+class Journals::CreateService
+  class Labelable < Association
+    def associated?
+      journable.respond_to?(:labels)
+    end
+
+    def cleanup_predecessor(predecessor, notes, cause)
+      cleanup_predecessor_for(predecessor,
+                              notes,
+                              cause,
+                              "label_journals",
+                              :journal_id,
+                              :id)
+    end
+
+    def insert_sql
+      sanitize(<<~SQL.squish, journable_id:, labelable_type: journable_class_name)
+        INSERT INTO
+          label_journals (
+            journal_id,
+            label_id
+          )
+        SELECT
+          #{id_from_inserted_journal_sql},
+          labelings.label_id
+        FROM labelings
+        WHERE
+          #{only_if_created_sql}
+          AND labelings.labelable_type = :labelable_type
+          AND labelings.labelable_id = :journable_id
+      SQL
+    end
+
+    def changes_sql
+      sanitize(<<~SQL.squish, journable_id:, labelable_type: journable_class_name)
+        SELECT
+          :journable_id AS journable_id
+        FROM
+          (
+            SELECT ARRAY_AGG(label_id ORDER BY label_id) AS labels
+            FROM labelings
+            WHERE labelings.labelable_type = :labelable_type
+              AND labelings.labelable_id = :journable_id
+          ) current_labels
+        CROSS JOIN
+          (
+            SELECT ARRAY_AGG(label_id ORDER BY label_id) AS labels
+            FROM label_journals
+            WHERE journal_id IN (SELECT id FROM max_journals)
+          ) journal_labels
+        WHERE
+          current_labels.labels IS DISTINCT FROM journal_labels.labels
+      SQL
+    end
+  end
+end
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 4d6063106457..7ac448863e52 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -509,6 +509,7 @@ en:
           title: "Working days"
           true: "include non-working days"
         journal_internal: Internal Journal
+        labels: "Labels"
         notify: "Notify" # used in custom actions
         observed_in_versions: "Observed in versions"
         parent: "Parent"
@@ -1163,6 +1164,9 @@ en:
       issue_priority:
         one: "Priority"
         other: "Priorities"
+      label:
+        one: "Label"
+        other: "Labels"
       ldap_auth_source:
         one: "LDAP connection"
         other: "LDAP connections"
diff --git a/db/migrate/20260914130000_create_label_journals.rb b/db/migrate/20260914130000_create_label_journals.rb
new file mode 100644
index 000000000000..8af04d0e0b16
--- /dev/null
+++ b/db/migrate/20260914130000_create_label_journals.rb
@@ -0,0 +1,39 @@
+# frozen_string_literal: true
+
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+class CreateLabelJournals < ActiveRecord::Migration[8.1]
+  def change
+    create_table :label_journals do |t| # rubocop:disable Rails/CreateTableWithTimestamps
+      t.belongs_to :journal, null: false, foreign_key: true
+      # No foreign key: journal snapshots must outlive deleted labels.
+      t.belongs_to :label, null: false
+    end
+  end
+end
diff --git a/lib/open_project/journal_formatter/joined_versions.rb b/lib/open_project/journal_formatter/joined_association.rb
similarity index 80%
rename from lib/open_project/journal_formatter/joined_versions.rb
rename to lib/open_project/journal_formatter/joined_association.rb
index fe63bb144784..76d7f20c620d 100644
--- a/lib/open_project/journal_formatter/joined_versions.rb
+++ b/lib/open_project/journal_formatter/joined_association.rb
@@ -28,11 +28,10 @@
 # See COPYRIGHT and LICENSE files for more details.
 #++
 
-# Base for formatters rendering the change to a set of versions referenced by a
-# work package. Each value is the sorted, comma-joined version ids (see
-# JournalChanges); every id is resolved to the version's name, dropping
-# versions that have been deleted or are no longer visible to the reader.
-class OpenProject::JournalFormatter::JoinedVersions < JournalFormatter::NamedAssociation
+# Base for formatters rendering the change to a set of associated records
+# referenced by the journable. Each value is the sorted, comma-joined ids;
+# deleted or non-visible records are dropped.
+class OpenProject::JournalFormatter::JoinedAssociation < JournalFormatter::NamedAssociation
   private
 
   def format_values(values, key)
diff --git a/lib/open_project/journal_formatter/labels.rb b/lib/open_project/journal_formatter/labels.rb
new file mode 100644
index 000000000000..4603302f137f
--- /dev/null
+++ b/lib/open_project/journal_formatter/labels.rb
@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+# Renders the change to the set of labels attached to a work package
+# (see JournalChanges#get_labels_changes).
+class OpenProject::JournalFormatter::Labels < OpenProject::JournalFormatter::JoinedAssociation
+end
diff --git a/lib/open_project/journal_formatter/observed_in_versions.rb b/lib/open_project/journal_formatter/observed_in_versions.rb
index f99881cf4ae8..ebfd3d71065c 100644
--- a/lib/open_project/journal_formatter/observed_in_versions.rb
+++ b/lib/open_project/journal_formatter/observed_in_versions.rb
@@ -30,5 +30,5 @@
 
 # Renders the change to the set of versions a work package was observed in
 # (see JournalChanges#get_observed_in_versions_changes).
-class OpenProject::JournalFormatter::ObservedInVersions < OpenProject::JournalFormatter::JoinedVersions
+class OpenProject::JournalFormatter::ObservedInVersions < OpenProject::JournalFormatter::JoinedAssociation
 end
diff --git a/lib/open_project/journal_formatter/target_versions.rb b/lib/open_project/journal_formatter/target_versions.rb
index 38a552689e6a..59b01d6a35ed 100644
--- a/lib/open_project/journal_formatter/target_versions.rb
+++ b/lib/open_project/journal_formatter/target_versions.rb
@@ -30,7 +30,7 @@
 
 # Renders the change to the set of target versions
 # (see JournalChanges#get_target_versions_changes).
-class OpenProject::JournalFormatter::TargetVersions < OpenProject::JournalFormatter::JoinedVersions
+class OpenProject::JournalFormatter::TargetVersions < OpenProject::JournalFormatter::JoinedAssociation
   private
 
   # While the multiple versions feature is inactive, the rest of the UI still
diff --git a/lib_static/plugins/acts_as_journalized/lib/journal_changes.rb b/lib_static/plugins/acts_as_journalized/lib/journal_changes.rb
index fd4c7cd6d46c..90225eff0457 100644
--- a/lib_static/plugins/acts_as_journalized/lib/journal_changes.rb
+++ b/lib_static/plugins/acts_as_journalized/lib/journal_changes.rb
@@ -48,6 +48,7 @@ def all_changes
       get_project_phases_changes,
       get_target_versions_changes,
       get_observed_in_versions_changes,
+      get_labels_changes,
       get_file_links_changes,
       get_participants_changes,
       get_agenda_items_changes
@@ -156,6 +157,16 @@ def get_observed_in_versions_changes
     { observed_in_versions: [old_value, new_value] }
   end
 
+  def get_labels_changes
+    return unless journable.respond_to?(:labels)
+
+    old_value = predecessor && joined_label_ids(predecessor)
+    new_value = joined_label_ids(self)
+    return if old_value == new_value
+
+    { labels: [old_value, new_value] }
+  end
+
   def get_file_links_changes
     return unless has_file_links?
 
@@ -217,6 +228,10 @@ def joined_observed_in_version_ids(journal)
     journal.observed_in_version_journals.map(&:version_id).sort.join(",").presence
   end
 
+  def joined_label_ids(journal)
+    journal.label_journals.map(&:label_id).sort.join(",").presence
+  end
+
   def participant_baseline_journal
     journals = journable.journals.to_a
     current_index = journals.index { |entry| entry.id == id }
diff --git a/spec/factories/journal/label_journal_factory.rb b/spec/factories/journal/label_journal_factory.rb
new file mode 100644
index 000000000000..207d4091c9eb
--- /dev/null
+++ b/spec/factories/journal/label_journal_factory.rb
@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+FactoryBot.define do
+  factory :journal_label_journal, class: "Journal::LabelJournal"
+end
diff --git a/spec/lib/open_project/journal_formatter/labels_spec.rb b/spec/lib/open_project/journal_formatter/labels_spec.rb
new file mode 100644
index 000000000000..b600aa5a19a3
--- /dev/null
+++ b/spec/lib/open_project/journal_formatter/labels_spec.rb
@@ -0,0 +1,100 @@
+# frozen_string_literal: true
+
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+require "spec_helper"
+
+RSpec.describe OpenProject::JournalFormatter::Labels do
+  describe "#render" do
+    let(:label) { build_stubbed(:label, name: "A") }
+    let(:other_label) { build_stubbed(:label, name: "B") }
+    let(:work_package) { build_stubbed(:work_package) }
+    let(:journal) { build_stubbed(:work_package_journal, journable: work_package) }
+    let(:instance) { described_class.new(journal) }
+    let(:label_text) { "<strong>Labels</strong>" }
+
+    before do
+      allow(Label).to receive(:find_by).and_return(nil)
+
+      [label, other_label].each do |l|
+        allow(Label).to receive(:find_by).with(id: l.id).and_return(l)
+      end
+    end
+
+    context "when setting labels" do
+      it "renders the label names as the new value" do
+        expect(instance.render(:labels, [nil, "#{label.id},#{other_label.id}"]))
+          .to eq(I18n.t(:text_journal_set_to, label: label_text, value: "<i>A, B</i>"))
+      end
+    end
+
+    context "when changing labels" do
+      it "renders the old and new label names" do
+        expect(instance.render(:labels, [label.id.to_s, other_label.id.to_s]))
+          .to eq(I18n.t(:text_journal_changed_plain,
+                        label: label_text,
+                        linebreak: nil,
+                        old: "<i>A</i>",
+                        new: "<i>B</i>"))
+      end
+    end
+
+    context "when removing all labels" do
+      it "renders the old label names as deleted" do
+        expect(instance.render(:labels, ["#{label.id},#{other_label.id}", nil]))
+          .to eq(I18n.t(:text_journal_deleted, label: label_text, old: "<strike><i>A, B</i></strike>"))
+      end
+    end
+
+    context "with a label that no longer exists" do
+      it "renders only the existing label names" do
+        expect(instance.render(:labels, [nil, "#{label.id},99999"]))
+          .to eq(I18n.t(:text_journal_set_to, label: label_text, value: "<i>A</i>"))
+      end
+    end
+
+    context "when setting labels that no longer exist" do
+      it "renders no detail" do
+        expect(instance.render(:labels, [nil, "99999,99998"]))
+          .to eq(I18n.t(:text_journal_deleted_no_detail, label: label_text))
+      end
+    end
+
+    context "with html: false" do
+      it "renders plain text" do
+        expect(instance.render(:labels, [label.id.to_s, other_label.id.to_s], html: false))
+          .to eq(I18n.t(:text_journal_changed_plain,
+                        label: "Labels",
+                        linebreak: nil,
+                        old: "A",
+                        new: "B"))
+      end
+    end
+  end
+end
diff --git a/spec/models/journable/with_historic_attributes_spec.rb b/spec/models/journable/with_historic_attributes_spec.rb
index 0e79855b5c04..0e1fa113bdb5 100644
--- a/spec/models/journable/with_historic_attributes_spec.rb
+++ b/spec/models/journable/with_historic_attributes_spec.rb
@@ -821,4 +821,107 @@ def update_observed_in_versions(*versions)
       end
     end
   end
+
+  describe "labels" do
+    shared_let(:label_a) { create(:label) }
+    shared_let(:label_b) { create(:label) }
+
+    let(:work_package) do
+      create(:work_package,
+             subject: "The labelled work package",
+             project:,
+             journals: {
+               created_at => {},
+               1.day.ago => {}
+             })
+    end
+
+    subject { described_class.wrap(work_package, timestamps:) }
+
+    def update_labels(*labels)
+      work_package.labels = labels
+      work_package.save!
+    end
+
+    def seed_baseline_label_journal(label)
+      create(:journal_label_journal, journal: work_package.journals.first, label:)
+    end
+
+    describe "#at_timestamp" do
+      it "returns the labels from the journal snapshot, not the current ones" do
+        seed_baseline_label_journal(label_a)
+        update_labels(label_a, label_b)
+
+        expect(subject.at_timestamp(Timestamp.parse("2022-01-01T00:00:00Z")).labels)
+          .to contain_exactly(label_a)
+        expect(work_package.reload.labels)
+          .to contain_exactly(label_a, label_b)
+      end
+
+      it "omits snapshotted labels that were deleted since" do
+        update_labels(label_a, label_b)
+        label_b.destroy!
+
+        # 1 hour in the future so the journal written by the update above is
+        # unambiguously in the past, regardless of sub-second timing.
+        expect(subject.at_timestamp(Timestamp.parse(1.hour.from_now.iso8601)).labels)
+          .to contain_exactly(label_a)
+      end
+    end
+
+    describe "#changed_at_timestamp" do
+      context "when a label was added" do
+        it "marks the labels as changed" do
+          update_labels(label_a, label_b)
+
+          expect(subject.changed_at_timestamp(Timestamp.parse("2022-01-01T00:00:00Z")))
+            .to contain_exactly("labels")
+        end
+      end
+
+      context "when one of several labels was removed" do
+        it "marks only the labels as changed" do
+          # Journal rows are stamped by the database clock, so a past removal
+          # can't be journalled directly; seed the baseline snapshot instead.
+          seed_baseline_label_journal(label_a)
+          seed_baseline_label_journal(label_b)
+          update_labels(label_a)
+
+          expect(subject.changed_at_timestamp(Timestamp.parse("2022-01-01T00:00:00Z")))
+            .to contain_exactly("labels")
+          expect(subject.send(:changes_at_timestamp, Timestamp.parse("2022-01-01T00:00:00Z"))["labels"])
+            .to eq([[label_a.id, label_b.id].sort.join(","), label_a.id.to_s])
+        end
+      end
+
+      context "when all labels were removed" do
+        it "marks the labels as changed" do
+          seed_baseline_label_journal(label_a)
+          update_labels
+
+          expect(subject.changed_at_timestamp(Timestamp.parse("2022-01-01T00:00:00Z")))
+            .to contain_exactly("labels")
+          expect(subject.send(:changes_at_timestamp, Timestamp.parse("2022-01-01T00:00:00Z"))["labels"])
+            .to eq([label_a.id.to_s, nil])
+        end
+      end
+
+      context "when the label set is unchanged" do
+        it "reports no label change" do
+          expect(subject.changed_at_timestamp(Timestamp.parse("2022-01-01T00:00:00Z")))
+            .to be_empty
+        end
+      end
+    end
+
+    describe "#changes_at_timestamp" do
+      it "reports the joined old and new label ids" do
+        seed_baseline_label_journal(label_a)
+        update_labels(label_a, label_b)
+
+        expect(subject.send(:changes_at_timestamp, Timestamp.parse("2022-01-01T00:00:00Z"))["labels"])
+          .to eq([label_a.id.to_s, [label_a.id, label_b.id].sort.join(",")])
+      end
+    end
+  end
 end
diff --git a/spec/models/journal/label_journal_spec.rb b/spec/models/journal/label_journal_spec.rb
new file mode 100644
index 000000000000..6d2ea252406f
--- /dev/null
+++ b/spec/models/journal/label_journal_spec.rb
@@ -0,0 +1,51 @@
+# frozen_string_literal: true
+
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+require "spec_helper"
+
+RSpec.describe Journal::LabelJournal do
+  it "belongs to a label" do
+    expect(described_class.reflect_on_association(:label).macro).to eq(:belongs_to)
+  end
+
+  it "uses the label_journals table" do
+    expect(described_class.table_name).to eq("label_journals")
+  end
+
+  it "keeps its rows when the label is destroyed" do
+    journal = create(:work_package_journal)
+    label = create(:label)
+    label_journal = described_class.create!(journal:, label:)
+
+    label.destroy!
+
+    expect(label_journal.reload.label_id).to eq(label.id)
+  end
+end
diff --git a/spec/models/work_package/work_package_acts_as_journalized_spec.rb b/spec/models/work_package/work_package_acts_as_journalized_spec.rb
index c417f6eddb23..73f7b78e45c1 100644
--- a/spec/models/work_package/work_package_acts_as_journalized_spec.rb
+++ b/spec/models/work_package/work_package_acts_as_journalized_spec.rb
@@ -576,6 +576,142 @@ def set_target_versions(versions)
       end
     end
 
+    context "on label changes", with_settings: { journal_aggregation_time_minutes: 0 } do
+      shared_let(:label) { create(:label) }
+      shared_let(:other_label) { create(:label) }
+
+      shared_let(:journable) do
+        create(:work_package)
+      end
+
+      def set_labels(labels)
+        journable.labelings.destroy_all
+        labels.each { journable.labelings.create!(label: it) }
+        journable.save!
+      end
+
+      context "when setting labels" do
+        it "creates a new journal listing the labels in the details" do
+          expect { set_labels([label, other_label]) }
+            .to change { journable.journals.count }.by(1)
+
+          expect(journable.last_journal.details["labels"])
+            .to eq([nil, [label.id, other_label.id].sort.join(",")])
+        end
+
+        it "touches the journable to match the journal's timestamp" do
+          expect { set_labels([label]) }
+            .to change { journable.reload.updated_at }
+
+          expect(journable.updated_at).to eq(journable.last_journal.updated_at)
+        end
+      end
+
+      context "on work package creation" do
+        it "creates an initial journal listing the labels in the details" do
+          work_package = create(:work_package, labels: [label])
+
+          expect(work_package.journals.count).to eq(1)
+          expect(work_package.last_journal.details["labels"])
+            .to eq([nil, label.id.to_s])
+          expect(Journal::LabelJournal.where(journal_id: work_package.last_journal.id).count)
+            .to eq(1)
+        end
+      end
+
+      context "when replacing a label" do
+        before do
+          set_labels([label])
+        end
+
+        it "creates a new journal with the old and new labels in the details" do
+          expect { set_labels([other_label]) }
+            .to change { journable.journals.count }.by(1)
+
+          expect(journable.last_journal.details["labels"])
+            .to eq([label.id.to_s, other_label.id.to_s])
+        end
+      end
+
+      context "when removing all labels" do
+        before do
+          set_labels([label])
+        end
+
+        it "creates a new journal with an empty new value in the details" do
+          expect { set_labels([]) }
+            .to change { journable.journals.count }.by(1)
+
+          expect(journable.last_journal.details["labels"])
+            .to eq([label.id.to_s, nil])
+        end
+      end
+
+      context "when saving with unchanged labels" do
+        before do
+          set_labels([label])
+        end
+
+        it "creates no journal and does not touch the journable" do
+          expect { set_labels([label]) }
+            .to not_change { journable.journals.count }
+            .and(not_change { journable.reload.updated_at })
+        end
+      end
+
+      context "when another labelable shares the work package's id" do
+        it "journals only the work package's own labels" do
+          Labeling.create!(label:, labelable_type: "Project", labelable_id: journable.id)
+
+          expect { set_labels([other_label]) }
+            .to change { journable.journals.count }.by(1)
+
+          expect(journable.last_journal.details["labels"])
+            .to eq([nil, other_label.id.to_s])
+        end
+      end
+
+      context "within aggregation time", with_settings: { journal_aggregation_time_minutes: 5 } do
+        # The initial journal lies outside the aggregation window so that only
+        # the journals created by the examples can aggregate with each other.
+        shared_let(:journable) do
+          create(:work_package,
+                 subject: "Initial subject",
+                 journals: { 10.minutes.ago => { user: } })
+        end
+
+        context "when changing labels again" do
+          before do
+            set_labels([label])
+          end
+
+          it "aggregates into the previous journal with cumulative details" do
+            expect { set_labels([label, other_label]) }
+              .not_to change { journable.journals.count }
+
+            expect(journable.last_journal.details["labels"])
+              .to eq([nil, [label.id, other_label.id].sort.join(",")])
+          end
+        end
+
+        context "when changing labels shortly after another change" do
+          before do
+            journable.update!(subject: "Changed subject")
+          end
+
+          it "aggregates into one journal capturing both changes" do
+            expect { set_labels([label]) }
+              .not_to change { journable.journals.count }
+
+            expect(journable.last_journal.details["subject"])
+              .to eq(["Initial subject", "Changed subject"])
+            expect(journable.last_journal.details["labels"])
+              .to eq([nil, label.id.to_s])
+          end
+        end
+      end
+    end
+
     context "on observed in version changes", with_settings: { journal_aggregation_time_minutes: 0 } do
       shared_let(:journable) do
         create(:work_package)
diff --git a/spec/services/journals/create_service/association_spec.rb b/spec/services/journals/create_service/association_spec.rb
index a6ccd0e9ef12..c5babbf1ce4b 100644
--- a/spec/services/journals/create_service/association_spec.rb
+++ b/spec/services/journals/create_service/association_spec.rb
@@ -65,11 +65,20 @@
       allow(journable).to receive(:respond_to?).with(:file_links).and_return(false)
       allow(journable).to receive(:respond_to?).with(:agenda_items).and_return(false)
       allow(journable).to receive(:respond_to?).with(:phases).and_return(false)
+      allow(journable).to receive(:respond_to?).with(:labels).and_return(false)
 
       associations = described_class.for(journable)
       expect(associations.map(&:class)).to include(Journals::CreateService::Attachable)
     end
 
+    it "includes Labelable for a journable that responds to labels" do
+      journable = instance_double(WorkPackage, customizable?: false, respond_to?: false)
+      allow(journable).to receive(:respond_to?).with(:labels).and_return(true)
+
+      associations = described_class.for(journable)
+      expect(associations.map(&:class)).to include(Journals::CreateService::Labelable)
+    end
+
     it "excludes associations whose #associated? returns false" do
       journable = instance_double(WorkPackage, customizable?: false, respond_to?: false)
       allow(journable).to receive(:respond_to?).and_return(false)