diff --git a/.changeset/happy-jars-joke.md b/.changeset/happy-jars-joke.md
new file mode 100644
index 0000000000..69a65c4f89
--- /dev/null
+++ b/.changeset/happy-jars-joke.md
@@ -0,0 +1,5 @@
+---
+'@lion/ui': patch
+---
+
+Added support for cross-root registration by adding a flag to composed property of form-element-register event.
diff --git a/packages/ui/components/form-core/src/registration/FormRegisteringMixin.js b/packages/ui/components/form-core/src/registration/FormRegisteringMixin.js
index 15c14a37c1..c8fb4a31f8 100644
--- a/packages/ui/components/form-core/src/registration/FormRegisteringMixin.js
+++ b/packages/ui/components/form-core/src/registration/FormRegisteringMixin.js
@@ -28,6 +28,19 @@ const FormRegisteringMixinImplementation = superclass =>
        * @type {FormRegistrarHost | undefined}
        */
       this._parentFormGroup = undefined;
+      /**
+       * To encourage accessibility best practices, `form-element-register` events
+       * do not pierce through shadow roots. This forces the developer to create form groups and fieldsets that automatically allow the creation of accessible relationships in the same dom tree.
+      Use this option if you know what you're doing. It will then be possible to nest FormControls
+      inside shadow dom. See https://lion-web.netlify.app/fundamentals/rationales/accessibility/#shadow-roots-and-accessibility
+      */
+      this.allowCrossRootRegistration = false;
+    }
+
+    static get properties() {
+      return {
+        allowCrossRootRegistration: { type: Boolean, attribute: 'allow-cross-root-registration' },
+      };
     }
 
     connectedCallback() {
@@ -36,6 +49,7 @@ const FormRegisteringMixinImplementation = superclass =>
         new CustomEvent('form-element-register', {
           detail: { element: this },
           bubbles: true,
+          composed: Boolean(this.allowCrossRootRegistration),
         }),
       );
     }
diff --git a/packages/ui/components/form-core/test-suites/FormRegistrationMixins.suite.js b/packages/ui/components/form-core/test-suites/FormRegistrationMixins.suite.js
index f873983914..71864f515e 100644
--- a/packages/ui/components/form-core/test-suites/FormRegistrationMixins.suite.js
+++ b/packages/ui/components/form-core/test-suites/FormRegistrationMixins.suite.js
@@ -1,11 +1,12 @@
-import { LitElement } from 'lit';
 import { uuid } from '@lion/ui/core.js';
-import { defineCE, expect, fixture, html, unsafeStatic } from '@open-wc/testing';
 import {
   FormRegisteringMixin,
   FormRegistrarMixin,
   FormRegistrarPortalMixin,
 } from '@lion/ui/form-core.js';
+import { defineCE, expect, fixture, html, unsafeStatic } from '@open-wc/testing';
+import { LitElement } from 'lit';
+import sinon from 'sinon';
 
 /**
  * @typedef {Object} customConfig
@@ -256,6 +257,60 @@ export const runRegistrationSuite = customConfig => {
       ]);
     });
 
+    describe('FormRegisteringMixin', () => {
+      it('propagates the form-element-register event through the shadowDom', async () => {
+        const eventSpy = sinon.spy();
+        const withShadowFormControlStr = defineCE(
+          class extends FormRegistrarMixin(LitElement) {
+            render() {
+              return html`
+              <${childTag}
+                id="child"
+                @form-element-register=${eventSpy}
+                allow-cross-root-registration
+              >
+              </${childTag}>`;
+            }
+          },
+        );
+        const withShadowFormControlTag = unsafeStatic(withShadowFormControlStr);
+
+        const el = /** @type {RegistrarClass} */ (
+          await fixture(html`
+            <${withShadowFormControlTag}>
+            </${withShadowFormControlTag}>
+          `)
+        );
+
+        expect(eventSpy).to.have.been.calledOnce;
+        expect(eventSpy.getCall(0).args[0].composed).to.equal(true);
+        expect(el.formElements).to.deep.equal([el.shadowRoot?.querySelector('#child')]);
+      });
+      it('dispatches the form-element-register event with compose true if allowCrossRootRegistration is set', async () => {
+        const eventSpy = sinon.spy();
+        /** @type {RegisteringClass} */ (
+          await fixture(html`
+            <${childTag}
+              @form-element-register=${eventSpy}
+              allow-cross-root-registration
+            >
+            </${childTag}>
+          `)
+        );
+        expect(eventSpy).to.have.been.calledOnce;
+        expect(eventSpy.getCall(0).args[0].composed).to.equal(true);
+      });
+      it('dispatches the form-element-register event with compose false if allowCrossRootRegistration is not set', async () => {
+        const eventSpy = sinon.spy();
+        /** @type {RegisteringClass} */ (
+          await fixture(html`
+            <${childTag} @form-element-register=${eventSpy}></${childTag}>
+          `)
+        );
+        expect(eventSpy).to.have.been.calledOnce;
+        expect(eventSpy.getCall(0).args[0].composed).to.equal(false);
+      });
+    });
     describe('FormRegistrarPortalMixin', () => {
       it('forwards registrations to the .registrationTarget', async () => {
         const el = /** @type {RegistrarClass} */ (
diff --git a/packages/ui/components/form-core/types/registration/FormRegisteringMixinTypes.ts b/packages/ui/components/form-core/types/registration/FormRegisteringMixinTypes.ts
index df896ddd58..2ec4ba313f 100644
--- a/packages/ui/components/form-core/types/registration/FormRegisteringMixinTypes.ts
+++ b/packages/ui/components/form-core/types/registration/FormRegisteringMixinTypes.ts
@@ -1,5 +1,5 @@
-import { LitElement } from 'lit';
 import { Constructor } from '@open-wc/dedupe-mixin';
+import { LitElement } from 'lit';
 
 import { FormRegistrarHost } from './FormRegistrarMixinTypes.js';
 
@@ -8,6 +8,14 @@ export declare class FormRegisteringHost {
    * The name the host is registered with to a parent
    */
   name: string;
+  /**
+   * To encourage accessibility best practices, `form-element-register` events
+   * do not pierce through shadow roots. This forces the developer to create form groups and fieldsets that
+   * automatically allow the creation of accessible relationships in the same dom tree.
+   * Use this option if you know what you're doing. It will then be possible to nest FormControls
+   * inside shadow dom. See https://lion-web.netlify.app/fundamentals/rationales/accessibility#shadow-roots-and-accessibility
+   */
+  allowCrossRootRegistration: boolean;
 
   /**
    * The registrar this FormControl registers to, Usually a descendant of FormGroup or