diff --git a/README.md b/README.md
index 8e02d68..42dad74 100644
--- a/README.md
+++ b/README.md
@@ -25,8 +25,9 @@ Create a YAML config file (see [`config.yaml`](config.yaml) for a template):
 paths:
   - /path/to/data
 
-# Unix group whose members' subdirectories should be reported (optional)
-group: your_group_name
+# Unix groups whose members' subdirectories should be reported (optional)
+groups:
+  - your_group_name
 
 # Shell-style glob patterns for files/directories to exclude (optional)
 ignore:
@@ -37,7 +38,7 @@ ignore:
 | Key | Description |
 |---|---|
 | `paths` | List of top-level paths to scan (required) |
-| `group` | Unix group name; enables group mode (optional, overridden by `--group`) |
+| `groups` | List of Unix group names; enables group mode (optional, overridden by `--groups`) |
 | `ignore` | Glob patterns matched against base names to exclude from all scans |
 
 ## Usage
@@ -49,7 +50,7 @@ python3 ontrack.py --config config.yaml [OPTIONS]
 | Option | Description |
 |---|---|
 | `--config FILE` | Path to the YAML config file (default: `config.yaml`) |
-| `--group GROUP` | Unix group name; overrides the `group` key in the config file |
+| `--groups GROUP [GROUP ...]` | One or more Unix group names; overrides the `groups` key in the config file |
 | `--light` | Skip file-count and size scanning; only report directory and owner |
 | `--progress` | Show progress bars while scanning |
 | `--output FILE` | Write the report as YAML to `FILE` instead of printing to stdout |
@@ -62,10 +63,10 @@ python3 ontrack.py --config config.yaml [OPTIONS]
 python3 ontrack.py --config config.yaml
 ```
 
-**Group mode** — for each configured directory, finds and reports subdirectories owned by members of the specified Unix group. Descends until a directory containing at least one file is found:
+**Group mode** — for each configured directory, finds and reports subdirectories owned by members of the specified Unix groups. Descends until a directory containing at least one file is found:
 
 ```bash
-python3 ontrack.py --config config.yaml --group researchers
+python3 ontrack.py --config config.yaml --groups researchers
 ```
 
 ## Example Output
diff --git a/ontrack.py b/ontrack.py
index b07c212..ee7686b 100644
--- a/ontrack.py
+++ b/ontrack.py
@@ -346,7 +346,7 @@ def report_directory(
     print(f"Directory : {entry['directory']}")
     print(f"Username  : {entry['username']}")
     if "groups" in entry:
-        print(f"Groups    : {', '.join(entry['groups'])}")
+        print(f"Group     : {', '.join(entry['groups'])}")
     if "file_count" in entry:
         print(f"Files     : {entry['file_count']}")
         print(f"Total size: {entry['total_size_human']}")
diff --git a/tests/test_ontrack.py b/tests/test_ontrack.py
index 29c0b78..9c9767d 100644
--- a/tests/test_ontrack.py
+++ b/tests/test_ontrack.py
@@ -278,7 +278,7 @@ def test_get_directory_stats_group_excludes_files():
 
 
 def test_report_directory_with_group(capsys):
-    """report_directory prints the Groups line when groups are supplied."""
+    """report_directory prints the Group line when groups are supplied."""
     current_gid = os.getgid()
     group_name = grp.getgrgid(current_gid).gr_name
 
@@ -288,19 +288,17 @@ def test_report_directory_with_group(capsys):
 
         report_directory(tmpdir, groups=[group_name])
         captured = capsys.readouterr()
-        assert "Groups" in captured.out
+        assert "Group" in captured.out
         assert group_name in captured.out
-
-
 def test_report_directory_without_group_no_group_line(capsys):
-    """report_directory does not print a Groups line when no groups are given."""
+    """report_directory does not print a Group line when no groups are given."""
     with tempfile.TemporaryDirectory() as tmpdir:
         with open(os.path.join(tmpdir, "sample.txt"), "w") as f:
             f.write("data")
 
         report_directory(tmpdir)
         captured = capsys.readouterr()
-        assert "Groups" not in captured.out
+        assert "Group     :" not in captured.out
 
 
 # ---------------------------------------------------------------------------
@@ -326,7 +324,7 @@ def test_main_with_group(tmp_path, capsys):
     main(str(config_file), groups=[group_name])
     captured = capsys.readouterr()
     assert str(user_subdir) in captured.out
-    assert "Groups" in captured.out
+    assert "Group" in captured.out
     assert group_name in captured.out
 
 
@@ -356,7 +354,7 @@ def test_main_with_multiple_groups(tmp_path, capsys):
     main(str(config_file), groups=[group_name, second_group])
     captured = capsys.readouterr()
     assert str(user_subdir) in captured.out
-    assert "Groups" in captured.out
+    assert "Group" in captured.out
     assert group_name in captured.out