diff --git a/README.md b/README.md
index 2a7c3fc..b3679e9 100644
--- a/README.md
+++ b/README.md
@@ -52,6 +52,9 @@ options:
   --verbose             Display debug information for each request
 ```
 
+Set `OPENCAGE_GEOCODING_API_KEY` to avoid passing your API key on the command
+line. A supplied `--api-key` takes precedence over the environment variable.
+
 <img src="batch-progress.gif"/>
 
 See [`examples/addresses.csv`](examples/addresses.csv) for sample input.
diff --git a/opencage_cli/command_line.py b/opencage_cli/command_line.py
index 341a438..569ad0d 100644
--- a/opencage_cli/command_line.py
+++ b/opencage_cli/command_line.py
@@ -1,6 +1,7 @@
 import argparse
 import sys
 import io
+import os
 from pathlib import Path
 import re
 import csv
@@ -52,7 +53,12 @@ def parse_args(args):
         'reverse', help="Reverse geocode a file (input is coordinates, add full address)")
 
     for subparser in [subparser_forward, subparser_reverse]:
-        subparser.add_argument("--api-key", required=True, type=api_key_type, help="Your OpenCage API key")
+        subparser.add_argument(
+            "--api-key",
+            default=os.environ.get("OPENCAGE_GEOCODING_API_KEY"),
+            required="OPENCAGE_GEOCODING_API_KEY" not in os.environ,
+            type=api_key_type,
+            help="Your OpenCage API key (or OPENCAGE_GEOCODING_API_KEY environment variable)")
         subparser.add_argument(
             "--input",
             required=True,
diff --git a/test/cli/test_cli_args.py b/test/cli/test_cli_args.py
index 28b7726..339137e 100644
--- a/test/cli/test_cli_args.py
+++ b/test/cli/test_cli_args.py
@@ -61,6 +61,31 @@ def test_invalid_api_key(capfd):
     )
 
 
+def test_api_key_from_environment(monkeypatch):
+    monkeypatch.setenv("OPENCAGE_GEOCODING_API_KEY", "oc_gc_12345678901234567890123456789012")
+
+    args = parse_args([
+        "forward",
+        "--input", "test/fixtures/input.txt",
+        "--output", "test/fixtures/output.csv"
+    ])
+
+    assert args.api_key == "oc_gc_12345678901234567890123456789012"
+
+
+def test_command_line_api_key_overrides_environment(monkeypatch):
+    monkeypatch.setenv("OPENCAGE_GEOCODING_API_KEY", "oc_gc_12345678901234567890123456789012")
+
+    args = parse_args([
+        "forward",
+        "--api-key", "12345678901234567890123456789012",
+        "--input", "test/fixtures/input.txt",
+        "--output", "test/fixtures/output.csv"
+    ])
+
+    assert args.api_key == "12345678901234567890123456789012"
+
+
 def test_existing_output_file(capfd):
     assert_parse_args_error(
         [