diff --git a/README.md b/README.md
index a17d864..024f1d2 100644
--- a/README.md
+++ b/README.md
@@ -118,6 +118,10 @@ docksec -i myapp:latest --image-only --json
 # Write a SARIF report for GitHub Code Scanning
 docksec Dockerfile --scan-only --sarif
 
+# Save today's findings as a baseline, then only gate on new findings later
+docksec -i myapp:latest --image-only --baseline .docksec-baseline.json --update-baseline
+docksec -i myapp:latest --image-only --baseline .docksec-baseline.json --fail-on high
+
 # Reduce output to warnings, errors, and the result summary
 docksec Dockerfile --scan-only --quiet
 
@@ -171,6 +175,26 @@ directly on pull requests and in the Security tab:
 which report formats you've selected, since it targets CI/Code Scanning rather than
 local reading.
 
+### Baseline / ratchet mode
+
+`--baseline FILE` lets you adopt `--fail-on` on an existing project without a wall of
+pre-existing findings blocking every build. Run once with `--update-baseline` to snapshot
+today's findings, then commit the baseline file; from then on, `--fail-on` only gates on
+findings that aren't already in the baseline:
+
+```bash
+# Snapshot current findings (does not gate)
+docksec -i myapp:latest --image-only --baseline .docksec-baseline.json --update-baseline
+
+# Later runs only fail on NEW findings above the threshold
+docksec -i myapp:latest --image-only --baseline .docksec-baseline.json --fail-on high
+```
+
+Findings are matched by vulnerability ID, target, and package name, so the baseline stays
+valid as unrelated findings come and go. Re-run with `--update-baseline` whenever you want
+to accept the current state as the new baseline (e.g. after triaging and deciding to defer
+a finding).
+
 ### Exit codes
 
 DockSec uses CI-friendly exit codes so builds and shells can react to results:
diff --git a/docksec/baseline.py b/docksec/baseline.py
new file mode 100644
index 0000000..3efd45d
--- /dev/null
+++ b/docksec/baseline.py
@@ -0,0 +1,45 @@
+"""Baseline/ratchet mode: compare a scan's findings against a stored baseline
+so --fail-on only gates on newly introduced findings.
+
+The baseline file is a flat JSON list of finding fingerprints. A fingerprint
+identifies a finding by VulnerabilityID + Target + PkgName, which is stable
+across scans of the same Dockerfile/image even as unrelated findings appear
+or disappear.
+"""
+
+import json
+from typing import Dict, List
+
+
+def fingerprint(vuln: Dict) -> str:
+    """Build a stable identity for a finding from its VulnerabilityID, Target,
+    and PkgName, so the same underlying issue matches across scans."""
+    vuln_id = str(vuln.get("VulnerabilityID") or "UNKNOWN")
+    target = str(vuln.get("Target") or "")
+    pkg = str(vuln.get("PkgName") or "")
+    return f"{vuln_id}|{target}|{pkg}"
+
+
+def load_baseline(path: str) -> List[str]:
+    """Load a baseline file's fingerprints. Returns [] if the file doesn't exist."""
+    try:
+        with open(path, "r") as f:
+            data = json.load(f)
+    except FileNotFoundError:
+        return []
+    return list(data.get("fingerprints", []))
+
+
+def save_baseline(path: str, results: Dict) -> None:
+    """Write the current scan's findings to the baseline file as fingerprints."""
+    vulnerabilities = results.get("json_data", [])
+    fingerprints = sorted({fingerprint(v) for v in vulnerabilities})
+    with open(path, "w") as f:
+        json.dump({"fingerprints": fingerprints}, f, indent=2)
+
+
+def new_findings(results: Dict, baseline_fingerprints: List[str]) -> List[Dict]:
+    """Return the findings in results that are not present in the baseline."""
+    baseline_set = set(baseline_fingerprints)
+    vulnerabilities = results.get("json_data", [])
+    return [v for v in vulnerabilities if fingerprint(v) not in baseline_set]
diff --git a/docksec/cli.py b/docksec/cli.py
index 5b01012..ee6bb63 100644
--- a/docksec/cli.py
+++ b/docksec/cli.py
@@ -58,6 +58,8 @@ def main() -> None:
     parser.add_argument('--output-dir', dest='output_dir', metavar='DIR', help='Directory to write reports to (default: ~/.docksec/results or DOCKSEC_RESULTS_DIR)')
     parser.add_argument('--json', dest='json_stdout', action='store_true', help='Print scan results as JSON to stdout (no report files unless --format is also given)')
     parser.add_argument('--sarif', dest='sarif', action='store_true', help='Write a SARIF 2.1.0 report for GitHub Code Scanning and other SARIF-compatible tools')
+    parser.add_argument('--baseline', dest='baseline', metavar='FILE', help='Path to a baseline file; with --fail-on, only findings not present in the baseline trigger the gate')
+    parser.add_argument('--update-baseline', dest='update_baseline', action='store_true', help='Write the current scan findings to --baseline instead of gating against it')
     parser.add_argument('--quiet', action='store_true', help='Reduce output to warnings, errors, and the result summary')
     parser.add_argument('--no-color', action='store_true', help='Disable colored output (also honors the NO_COLOR env var)')
     parser.add_argument('--version', action='version', version=f'DockSec {get_version()}')
@@ -140,6 +142,10 @@ def main() -> None:
     output_dir = args.output_dir or RESULTS_DIR
 
     # Validate argument combinations
+    if args.update_baseline and not args.baseline:
+        output.error("--update-baseline requires --baseline FILE")
+        sys.exit(2)
+
     if args.image_only and args.ai_only:
         output.error("--image-only and --ai-only cannot be used together (AI analysis requires a Dockerfile)")
         sys.exit(2)
@@ -358,14 +364,28 @@ def main() -> None:
                 _render_scan_summary(output, args, scanner, results, report_paths,
                                      run_ai, run_compose_analysis)
 
+            # --update-baseline: snapshot current findings and skip gating.
+            if args.update_baseline:
+                from docksec import baseline as baseline_mod
+                baseline_mod.save_baseline(args.baseline, results)
+                output.info(f"Baseline written to {args.baseline}")
+
             # --fail-on gate: flag findings at or above the chosen threshold.
-            if args.fail_on:
+            # With --baseline (and not --update-baseline), only findings not
+            # already present in the baseline count toward the gate.
+            if args.fail_on and not args.update_baseline:
                 triggering = _findings_at_or_above(results, args.fail_on)
+                if args.baseline:
+                    from docksec import baseline as baseline_mod
+                    baseline_fingerprints = baseline_mod.load_baseline(args.baseline)
+                    new_ids = {baseline_mod.fingerprint(v) for v in baseline_mod.new_findings(results, baseline_fingerprints)}
+                    triggering = [v for v in triggering if baseline_mod.fingerprint(v) in new_ids]
                 if triggering:
                     gate_triggered = True
+                    suffix = " (new since baseline)" if args.baseline else ""
                     output.warn(
-                        f"{len(triggering)} finding(s) at or above {args.fail_on} "
-                        f"(--fail-on {args.fail_on}) -> exit 1"
+                        f"{len(triggering)} finding(s) at or above {args.fail_on}"
+                        f"{suffix} (--fail-on {args.fail_on}) -> exit 1"
                     )
 
         except ValueError as e:
diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index 0f05c96..5f45677 100644
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -24,6 +24,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - `--json` flag: print scan results as a single JSON object to stdout for scripts and CI pipelines. All human-readable output (banner, sections, info/warn/error, the result summary) moves to stderr in `--json` mode, so stdout carries only the JSON payload. `--json` alone does not write report files; combine with `--format` to also write files.
 - `--sarif` flag: write a SARIF 2.1.0 report for GitHub Code Scanning and other SARIF-compatible tools. Independent of `--format`; findings map to one SARIF rule per unique vulnerability ID and one result per finding, with severity mapped to SARIF levels (`CRITICAL`/`HIGH` -> `error`, `MEDIUM` -> `warning`, `LOW`/`UNKNOWN` -> `note`).
 - GitHub Action inputs for the new CLI flags: `output_dir`, `severity`, `fail_on`, `format`, `sarif`.
+- `--baseline <file>` and `--update-baseline` flags for ratchet-mode adoption: `--update-baseline` snapshots the current scan's findings to the baseline file; subsequent runs with `--baseline` and `--fail-on` only gate on findings not already present in the baseline, so `--fail-on` can be adopted on existing projects without pre-existing findings blocking every build. Findings are matched by vulnerability ID, target, and package name.
 
 ### Changed
 - **Cleaner terminal output**: internal logs now write to `stderr` instead of `stdout` and stay quiet in CLI mode, so raw location-tagged log lines no longer interleave with the tool's user-facing messages. Set `DOCKSEC_LOG_LEVEL` to restore verbose logging.
diff --git a/tests/test_baseline.py b/tests/test_baseline.py
new file mode 100644
index 0000000..23a3da4
--- /dev/null
+++ b/tests/test_baseline.py
@@ -0,0 +1,84 @@
+import json
+import os
+import tempfile
+import unittest
+
+from docksec import baseline
+
+
+class TestFingerprint(unittest.TestCase):
+    def test_fingerprint_stable_for_same_finding(self):
+        v = {"VulnerabilityID": "CVE-2024-1", "Target": "app", "PkgName": "openssl"}
+        self.assertEqual(baseline.fingerprint(v), baseline.fingerprint(dict(v)))
+
+    def test_fingerprint_differs_on_any_field(self):
+        base = {"VulnerabilityID": "CVE-2024-1", "Target": "app", "PkgName": "openssl"}
+        other = {"VulnerabilityID": "CVE-2024-2", "Target": "app", "PkgName": "openssl"}
+        self.assertNotEqual(baseline.fingerprint(base), baseline.fingerprint(other))
+
+    def test_fingerprint_handles_missing_fields(self):
+        self.assertEqual(baseline.fingerprint({}), "UNKNOWN||")
+
+
+class TestLoadSaveBaseline(unittest.TestCase):
+    def test_load_missing_file_returns_empty(self):
+        self.assertEqual(baseline.load_baseline("/nonexistent/path/baseline.json"), [])
+
+    def test_save_then_load_round_trips(self):
+        results = {
+            "json_data": [
+                {"VulnerabilityID": "CVE-1", "Target": "a", "PkgName": "pkg1", "Severity": "HIGH"},
+                {"VulnerabilityID": "CVE-2", "Target": "a", "PkgName": "pkg2", "Severity": "LOW"},
+            ]
+        }
+        with tempfile.TemporaryDirectory() as d:
+            path = os.path.join(d, "baseline.json")
+            baseline.save_baseline(path, results)
+            loaded = baseline.load_baseline(path)
+            self.assertEqual(len(loaded), 2)
+            self.assertIn(baseline.fingerprint(results["json_data"][0]), loaded)
+
+    def test_save_dedupes_identical_findings(self):
+        vuln = {"VulnerabilityID": "CVE-1", "Target": "a", "PkgName": "pkg1", "Severity": "HIGH"}
+        results = {"json_data": [vuln, dict(vuln)]}
+        with tempfile.TemporaryDirectory() as d:
+            path = os.path.join(d, "baseline.json")
+            baseline.save_baseline(path, results)
+            with open(path) as f:
+                data = json.load(f)
+            self.assertEqual(len(data["fingerprints"]), 1)
+
+    def test_save_writes_valid_json_structure(self):
+        with tempfile.TemporaryDirectory() as d:
+            path = os.path.join(d, "baseline.json")
+            baseline.save_baseline(path, {"json_data": []})
+            with open(path) as f:
+                data = json.load(f)
+            self.assertEqual(data, {"fingerprints": []})
+
+
+class TestNewFindings(unittest.TestCase):
+    def test_new_findings_excludes_baselined(self):
+        v1 = {"VulnerabilityID": "CVE-1", "Target": "a", "PkgName": "pkg1"}
+        v2 = {"VulnerabilityID": "CVE-2", "Target": "a", "PkgName": "pkg2"}
+        results = {"json_data": [v1, v2]}
+        baseline_fps = [baseline.fingerprint(v1)]
+        result = baseline.new_findings(results, baseline_fps)
+        self.assertEqual(result, [v2])
+
+    def test_new_findings_all_new_when_baseline_empty(self):
+        v1 = {"VulnerabilityID": "CVE-1", "Target": "a", "PkgName": "pkg1"}
+        results = {"json_data": [v1]}
+        self.assertEqual(baseline.new_findings(results, []), [v1])
+
+    def test_new_findings_empty_when_all_baselined(self):
+        v1 = {"VulnerabilityID": "CVE-1", "Target": "a", "PkgName": "pkg1"}
+        results = {"json_data": [v1]}
+        self.assertEqual(baseline.new_findings(results, [baseline.fingerprint(v1)]), [])
+
+    def test_new_findings_handles_no_findings(self):
+        self.assertEqual(baseline.new_findings({"json_data": []}, []), [])
+
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/tests/test_cli.py b/tests/test_cli.py
index 807a577..a7765a8 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -1,5 +1,6 @@
 """Unit tests for CLI arguments and flags."""
 import unittest
+import json
 import os
 import sys
 import tempfile
@@ -572,5 +573,80 @@ def test_sarif_flag_does_not_affect_default_format_bundle(self):
         self.assertEqual(kwargs.get('formats'), ['json'])
 
 
+class TestBaselineGate(unittest.TestCase):
+    """Test cases for --baseline / --update-baseline wiring in the CLI."""
+
+    def setUp(self):
+        self._tmpdir = tempfile.TemporaryDirectory()
+        self.addCleanup(self._tmpdir.cleanup)
+        self.baseline_path = os.path.join(self._tmpdir.name, 'baseline.json')
+
+    def _run_image_only_with(self, findings, extra_argv=None):
+        from docksec.cli import main
+
+        argv = ['docksec', '--image-only', '-i', 'test:latest'] + (extra_argv or [])
+        with patch('sys.argv', argv), \
+             patch('docksec.docker_scanner.DockerSecurityScanner') as cls:
+            scanner = Mock()
+            cls.return_value = scanner
+            scanner.run_image_only_scan.return_value = {
+                'json_data': [
+                    {"VulnerabilityID": f"CVE-{i}", "Target": "app", "PkgName": "pkg", "Severity": s}
+                    for i, s in enumerate(findings)
+                ],
+                'dockerfile_scan': {'skipped': True},
+                'image_scan': {'skipped': False},
+                'scan_mode': 'image_only',
+            }
+            scanner.get_security_score.return_value = 80.0
+            scanner.generate_all_reports.return_value = {'json': 'x'}
+            scanner.RESULTS_DIR = '/tmp'
+            code = 0
+            try:
+                main()
+            except SystemExit as e:
+                code = e.code
+            return code
+
+    def test_update_baseline_without_baseline_flag_exits_2(self):
+        code = self._run_image_only_with(["HIGH"], ['--update-baseline'])
+        self.assertEqual(code, 2)
+
+    def test_update_baseline_writes_file_and_does_not_gate(self):
+        code = self._run_image_only_with(
+            ["CRITICAL"],
+            ['--baseline', self.baseline_path, '--update-baseline', '--fail-on', 'critical'],
+        )
+        self.assertEqual(code, 0)
+        self.assertTrue(os.path.isfile(self.baseline_path))
+        with open(self.baseline_path) as f:
+            data = json.load(f)
+        self.assertEqual(len(data['fingerprints']), 1)
+
+    def test_baseline_suppresses_previously_seen_findings(self):
+        # First run establishes the baseline.
+        self._run_image_only_with(
+            ["CRITICAL"], ['--baseline', self.baseline_path, '--update-baseline']
+        )
+        # Same finding again, now gated: should NOT trigger since it's baselined.
+        code = self._run_image_only_with(
+            ["CRITICAL"], ['--baseline', self.baseline_path, '--fail-on', 'critical']
+        )
+        self.assertEqual(code, 0)
+
+    def test_baseline_still_gates_on_new_findings(self):
+        # Baseline has no findings.
+        self._run_image_only_with([], ['--baseline', self.baseline_path, '--update-baseline'])
+        # A new CRITICAL finding appears: should trigger the gate.
+        code = self._run_image_only_with(
+            ["CRITICAL"], ['--baseline', self.baseline_path, '--fail-on', 'critical']
+        )
+        self.assertEqual(code, 1)
+
+    def test_fail_on_without_baseline_gates_normally(self):
+        code = self._run_image_only_with(["CRITICAL"], ['--fail-on', 'critical'])
+        self.assertEqual(code, 1)
+
+
 if __name__ == '__main__':
     unittest.main()