diff --git a/modules/.submodules.json b/modules/.submodules.json
index 5aa83c64376..a1b2971bfea 100644
--- a/modules/.submodules.json
+++ b/modules/.submodules.json
@@ -18,6 +18,7 @@
       "fabrickIdSystem",
       "freepassIdSystem",
       "ftrackIdSystem",
+      "gemiusIdSystem",
       "gravitoIdSystem",
       "growthCodeIdSystem",
       "hadronIdSystem",
diff --git a/modules/gemiusIdSystem.md b/modules/gemiusIdSystem.md
new file mode 100644
index 00000000000..e285a673db6
--- /dev/null
+++ b/modules/gemiusIdSystem.md
@@ -0,0 +1,31 @@
+## Gemius User ID Submodule
+
+This module supports [Gemius](https://gemius.com/) customers in using Real Users ID (RUID) functionality.
+
+## Building Prebid.js with Gemius User ID Submodule
+
+To build Prebid.js with the `gemiusIdSystem` module included:
+
+```
+gulp build --modules=userId,gemiusIdSystem
+```
+
+### Prebid Configuration
+
+You can configure this submodule in your `userSync.userIds[]` configuration:
+
+```javascript
+pbjs.setConfig({
+    userSync: {
+        userIds: [{
+            name: 'gemiusId',
+            storage: {
+                name: 'pbjs_gemiusId',
+                type: 'cookie',
+                expires: 30,
+                refreshInSeconds: 3600
+            }
+        }]
+    }
+});
+```
diff --git a/modules/gemiusIdSystem.ts b/modules/gemiusIdSystem.ts
new file mode 100644
index 00000000000..e5e6d335857
--- /dev/null
+++ b/modules/gemiusIdSystem.ts
@@ -0,0 +1,122 @@
+import { logInfo, logError, isStr, getWindowTop, canAccessWindowTop, getWindowSelf } from '../src/utils.js';
+import { submodule } from '../src/hook.js';
+import { AllConsentData } from "../src/consentHandler.ts";
+
+import type { IdProviderSpec } from './userId/spec.ts';
+
+const MODULE_NAME = 'gemiusId' as const;
+const GVLID = 328;
+const REQUIRED_PURPOSES = [1, 2, 3, 4, 7, 8, 9, 10];
+const LOG_PREFIX = 'Gemius User ID: ';
+
+const WAIT_FOR_PRIMARY_SCRIPT_MAX_TRIES = 8;
+const WAIT_FOR_PRIMARY_SCRIPT_INITIAL_WAIT_MS = 50;
+const GEMIUS_CMD_TIMEOUT = 8000;
+
+type SerializableId = string | Record<string, unknown>;
+type PrimaryScriptWindow = Window & {
+  gemius_cmd: (action: string, callback: (ruid: string, desc: { status: string }) => void) => void;
+};
+
+declare module './userId/spec' {
+  interface UserId {
+    gemiusId: string;
+  }
+  interface ProvidersToId {
+    gemiusId: 'gemiusId';
+  }
+}
+
+function getTopAccessibleWindow(): Window {
+  if (canAccessWindowTop()) {
+    return getWindowTop();
+  }
+
+  return getWindowSelf();
+}
+
+function retrieveId(primaryScriptWindow: PrimaryScriptWindow, callback: (id: SerializableId) => void): void {
+  let resultResolved = false;
+  let timeoutId: number | null = null;
+  const setResult = function (id?: SerializableId): void {
+    if (resultResolved) {
+      return;
+    }
+
+    resultResolved = true;
+    if (timeoutId) {
+      clearTimeout(timeoutId);
+      timeoutId = null;
+    }
+    callback(id);
+  }
+
+  timeoutId = setTimeout(() => {
+    logError(LOG_PREFIX + 'failed to get id, timeout');
+    timeoutId = null;
+    setResult();
+  }, GEMIUS_CMD_TIMEOUT);
+
+  try {
+    primaryScriptWindow.gemius_cmd('get_ruid', function (ruid, desc) {
+      if (desc.status === 'ok') {
+        setResult({id: ruid});
+      } else if (desc.status === 'no-consent') {
+        logInfo(LOG_PREFIX + 'failed to get id, no consent');
+        setResult({id: null});
+      } else {
+        logError(LOG_PREFIX + 'failed to get id, response: ' + desc.status);
+        setResult();
+      }
+    });
+  } catch (e) {
+    logError(LOG_PREFIX + 'failed to get id, error: ' + e);
+    setResult();
+  }
+}
+
+export const gemiusIdSubmodule: IdProviderSpec<typeof MODULE_NAME> = {
+  name: MODULE_NAME,
+  gvlid: GVLID,
+  decode(value) {
+    if (isStr(value?.['id'])) {
+      return {[MODULE_NAME]: value['id']};
+    }
+    return undefined;
+  },
+  getId(_, {gdpr: consentData}: Partial<AllConsentData> = {}) {
+    if (consentData && typeof consentData.gdprApplies === 'boolean' && consentData.gdprApplies) {
+      if (REQUIRED_PURPOSES.some(purposeId => !(consentData.vendorData?.purpose as any)?.consents?.[purposeId])) {
+        logInfo(LOG_PREFIX + 'getId, no consent');
+        return {id: {id: null}};
+      }
+    }
+
+    logInfo(LOG_PREFIX + 'getId');
+    return {
+      callback: function (callback) {
+        const win = getTopAccessibleWindow();
+
+        (function waitForPrimaryScript(tryCount = 1, nextWaitTime = WAIT_FOR_PRIMARY_SCRIPT_INITIAL_WAIT_MS) {
+          if (typeof win['gemius_cmd'] !== 'undefined') {
+            retrieveId(win as PrimaryScriptWindow, callback);
+          }
+
+          if (tryCount < WAIT_FOR_PRIMARY_SCRIPT_MAX_TRIES) {
+            setTimeout(() => waitForPrimaryScript(tryCount + 1, nextWaitTime * 2), nextWaitTime);
+          } else {
+            callback(undefined);
+          }
+        })();
+      }
+    };
+  },
+  eids: {
+    [MODULE_NAME]: {
+      source: 'gemius.com',
+      atype: '1',
+    },
+  }
+};
+
+submodule('userId', gemiusIdSubmodule);
diff --git a/modules/userId/eids.md b/modules/userId/eids.md
index 53567032175..f6f62229f53 100644
--- a/modules/userId/eids.md
+++ b/modules/userId/eids.md
@@ -335,6 +335,13 @@ userIdAsEids = [
             id: 'some-random-id-value',
             atype: 1
         }]
+    },
+    {
+        source: 'gemius.com'',
+        uids: [{
+            id: 'some-random-id-value',
+            atype: 1
+        }]
     }
 ]
 ```
diff --git a/modules/userId/userId.md b/modules/userId/userId.md
index 9aea3e8d533..9cc2ce5bf5c 100644
--- a/modules/userId/userId.md
+++ b/modules/userId/userId.md
@@ -137,7 +137,9 @@ pbjs.setConfig({
                   name: '__adm__admixer',
                   expires: 30
               }
-        },{
+        }, {
+            name: "gemiusId"
+        }, {
              name: "kpuid",
              params:{
                     accountid: 124 // example of account id
diff --git a/test/spec/modules/gemiusIdSystem_spec.js b/test/spec/modules/gemiusIdSystem_spec.js
new file mode 100644
index 00000000000..76c4549a321
--- /dev/null
+++ b/test/spec/modules/gemiusIdSystem_spec.js
@@ -0,0 +1,151 @@
+import { gemiusIdSubmodule } from 'modules/gemiusIdSystem.ts';
+import * as utils from 'src/utils.js';
+
+describe('GemiusId module', function () {
+  let getWindowTopStub;
+  let mockWindow;
+  let clock;
+
+  beforeEach(function () {
+    mockWindow = {
+      gemius_cmd: sinon.stub()
+    };
+    getWindowTopStub = sinon.stub(utils, 'getWindowTop').returns(mockWindow);
+  });
+
+  afterEach(function () {
+    getWindowTopStub.restore();
+    if (clock) {
+      clock.restore();
+      clock = undefined;
+    }
+  });
+
+  describe('gemiusIdSubmodule', function () {
+    it('should have the correct name', function () {
+      expect(gemiusIdSubmodule.name).to.equal('gemiusId');
+    });
+
+    it('should have correct eids configuration', function () {
+      expect(gemiusIdSubmodule.eids.gemiusId).to.deep.include({
+        source: 'gemius.com',
+        atype: '1'
+      });
+    });
+
+    it('should have correct gvlid', function () {
+      expect(gemiusIdSubmodule.gvlid).to.be.a('number');
+    });
+  });
+
+  describe('getId', function () {
+    const gdprConsentData = {
+      gdprApplies: true,
+      apiVersion: 2,
+      vendorData: {
+        purpose: {
+          consents: {
+            1: true,
+            2: false,
+            3: true, 4: true, 5: true, 6: true, 7: true, 8: true, 9: true, 10: true, 11: true
+          }
+        }
+      }
+    };
+
+    it('should return undefined if gemius_cmd is not available', function (done) {
+      clock = sinon.useFakeTimers();
+      getWindowTopStub.returns({});
+
+      gemiusIdSubmodule.getId().callback((resultId) => {
+        expect(resultId).to.be.undefined;
+        done();
+      });
+
+      clock.tick(6400);
+    });
+
+    it('should return null id if no consent', function () {
+      const result = gemiusIdSubmodule.getId({}, {
+        gdpr: gdprConsentData
+      });
+      expect(result).to.deep.equal({id: {id: null}});
+    });
+
+    it('should return callback on consent', function () {
+      const result = gemiusIdSubmodule.getId({}, {
+        gdpr: utils.deepClone(gdprConsentData).vendorData.purpose.consents["2"] = true
+      });
+      expect(result).to.have.property('callback');
+      expect(result.callback).to.be.a('function');
+    });
+
+    it('should return callback when gemius_cmd is available', function () {
+      const result = gemiusIdSubmodule.getId();
+      expect(result).to.have.property('callback');
+      expect(result.callback).to.be.a('function');
+    });
+
+    it('should call gemius_cmd with correct parameters', function (done) {
+      mockWindow.gemius_cmd.callsFake((command, callback) => {
+        expect(command).to.equal('get_ruid');
+        expect(callback).to.be.a('function');
+
+        const testRuid = 'test-ruid-123';
+        const statusOk = {status: 'ok'};
+        callback(testRuid, statusOk);
+      });
+
+      gemiusIdSubmodule.getId().callback((resultId) => {
+        expect(resultId).to.deep.equal({id: 'test-ruid-123'});
+        expect(mockWindow.gemius_cmd.calledOnce).to.be.true;
+        done();
+      });
+    });
+
+    it('should handle gemius_cmd throwing an error', function (done) {
+      mockWindow.gemius_cmd.callsFake(() => {
+        throw new Error();
+      });
+
+      const result = gemiusIdSubmodule.getId();
+      result.callback((resultId) => {
+        expect(resultId).to.be.undefined;
+        done();
+      });
+    });
+
+    it('should handle gemius_cmd not calling callback', function (done) {
+      const clock = sinon.useFakeTimers();
+
+      mockWindow.gemius_cmd.callsFake((command, callback) => {
+        // Don't call callback to simulate timeout/no response
+      });
+
+      gemiusIdSubmodule.getId().callback((resultId) => {
+        expect(resultId).to.be.undefined;
+        clock.restore();
+        done();
+      });
+
+      clock.tick(8100);
+    });
+  });
+
+  describe('decode', function () {
+    it('should return object with gemiusId when value exists', function () {
+      const result = gemiusIdSubmodule.decode({id: 'test-gemius-id'});
+      expect(result).to.deep.equal({
+        gemiusId: 'test-gemius-id'
+      });
+    });
+
+    it('should return undefined when value is falsy', function () {
+      expect(gemiusIdSubmodule.decode('')).to.be.undefined;
+      expect(gemiusIdSubmodule.decode(null)).to.be.undefined;
+      expect(gemiusIdSubmodule.decode(undefined)).to.be.undefined;
+      expect(gemiusIdSubmodule.decode(0)).to.be.undefined;
+      expect(gemiusIdSubmodule.decode(false)).to.be.undefined;
+    });
+  });
+});