diff --git a/.all-contributorsrc b/.all-contributorsrc
index a7cd07aaf96d..3088b1880d80 100644
--- a/.all-contributorsrc
+++ b/.all-contributorsrc
@@ -1721,6 +1721,13 @@
       "name": "Zoë Gathercole",
       "avatar_url": "https://avatars.githubusercontent.com/u/56911544?v=4",
       "profile": "https://github.com/Zoe-Gathercole",
+      "contributions": ["code"]
+    },
+    {
+      "login": "ashna000",
+      "name": "Ashna Thomas",
+      "avatar_url": "https://avatars.githubusercontent.com/u/12691034?s=96&v=4",
+      "profile": "https://github.com/ashna000",
       "contributions": [
         "code"
       ]
diff --git a/README.md b/README.md
index 30d2bfc8a91a..3b7067b4ac91 100644
--- a/README.md
+++ b/README.md
@@ -321,6 +321,9 @@ check out our [Contributing Guide](/.github/CONTRIBUTING.md) and our
     <td align="center"><a href="https://github.com/Zoe-Gathercole"><img src="https://avatars.githubusercontent.com/u/56911544?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Zoë Gathercole</b></sub></a><br /><a href="https://github.com/carbon-design-system/carbon/commits?author=Zoe-Gathercole" title="Code">💻</a></td>
     <td align="center"><a href="https://github.com/a88zach"><img src="https://avatars.githubusercontent.com/u/1724822?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Zach Tindall</b></sub></a><br /><a href="https://github.com/carbon-design-system/carbon/commits?author=a88zach" title="Code">💻</a></td>
   </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/ashna000"><img src="https://avatars.githubusercontent.com/u/12691034?s=96&v=4?s=100" width="100px;" alt=""/><br /><sub><b>Ashna Thomas</b></sub></a><br /><a href="https://github.com/carbon-design-system/carbon/commits?author=ashna000" title="Code">💻</a></td>
+  </tr>
 </table>
 
 <!-- markdownlint-restore -->
diff --git a/packages/react/src/components/UIShell/__tests__/SideNav-test.js b/packages/react/src/components/UIShell/__tests__/SideNav-test.js
index 02d727ae319d..d3974e5300d4 100644
--- a/packages/react/src/components/UIShell/__tests__/SideNav-test.js
+++ b/packages/react/src/components/UIShell/__tests__/SideNav-test.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import { render, screen } from '@testing-library/react';
+import { render, screen, fireEvent } from '@testing-library/react';
 import React from 'react';
 import SideNav from '../SideNav';
 
@@ -15,8 +15,8 @@ Object.defineProperty(window, 'matchMedia', {
     matches: false,
     media: query,
     onchange: null,
-    addListener: jest.fn(), // deprecated
-    removeListener: jest.fn(), // deprecated
+    addListener: jest.fn(),
+    removeListener: jest.fn(),
     addEventListener: jest.fn(),
     removeEventListener: jest.fn(),
     dispatchEvent: jest.fn(),
@@ -36,6 +36,11 @@ describe('SideNav', () => {
     expect(container.childNodes.length).toBe(2);
   });
 
+  it('should not render an overlay if `isFixedNav` is true', () => {
+    const { container } = render(<SideNav aria-label="test" isFixedNav />);
+    expect(container.childNodes.length).toBe(1);
+  });
+
   it('should toggle the overlay-active class when `expanded` is true', () => {
     const { container } = render(<SideNav aria-label="test" expanded />);
     expect(container.firstChild).toHaveClass('cds--side-nav__overlay-active');
@@ -64,4 +69,269 @@ describe('SideNav', () => {
     render(<SideNav aria-label="test" ref={ref} />);
     expect(ref).toHaveBeenCalledWith(screen.getByRole('navigation'));
   });
+
+  it('should call onOverlayClick when overlay is clicked', () => {
+    const onOverlayClick = jest.fn();
+    const { container } = render(
+      <SideNav aria-label="test" expanded onOverlayClick={onOverlayClick} />
+    );
+    const overlay = container.firstChild;
+    fireEvent.click(overlay);
+    expect(onOverlayClick).toHaveBeenCalledTimes(1);
+  });
+
+  it('should not add focus or mouse listeners when disabled', () => {
+    const onToggle = jest.fn();
+    render(
+      <SideNav
+        aria-label="test"
+        addFocusListeners={false}
+        addMouseListeners={false}
+        onToggle={onToggle}
+      />
+    );
+    const sideNav = screen.getByRole('navigation');
+    fireEvent.focus(sideNav);
+    fireEvent.mouseEnter(sideNav);
+    expect(onToggle).not.toHaveBeenCalled();
+  });
+
+  it('should handle keyboard events like Escape', () => {
+    const onToggle = jest.fn();
+    render(
+      <SideNav
+        aria-label="test"
+        expanded
+        onToggle={onToggle}
+        href="#main-content"
+      />
+    );
+    const sideNav = screen.getByRole('navigation');
+    fireEvent.keyDown(sideNav, { key: 'Escape', keyCode: 27 });
+    expect(onToggle).toHaveBeenCalledWith(expect.anything(), false);
+  });
+
+  it('should correctly handle `isRail` when true', () => {
+    render(<SideNav aria-label="test" isRail />);
+    const sideNav = screen.getByRole('navigation');
+    expect(sideNav).toHaveClass('cds--side-nav--rail');
+  });
+
+  it('should correctly handle `isRail` when false', () => {
+    render(<SideNav aria-label="test" isRail={false} />);
+    const sideNav = screen.getByRole('navigation');
+    expect(sideNav).not.toHaveClass('cds--side-nav--rail');
+  });
+
+  it('should toggle the expanded state when uncontrolled', () => {
+    const { container } = render(<SideNav aria-label="test" />);
+    const sideNav = screen.getByRole('navigation');
+    fireEvent.focus(sideNav);
+    expect(container.firstChild).toHaveClass('cds--side-nav__overlay');
+  });
+
+  it('should handle children without throwing error', () => {
+    const { container } = render(
+      <SideNav aria-label="test">
+        <div>No Errors Here!</div>
+      </SideNav>
+    );
+    expect(container).toBeInTheDocument();
+  });
+
+  it('should pass isSideNavExpanded to Carbon SideNav children', () => {
+    const TestChild = React.forwardRef(({ isSideNavExpanded }, ref) => (
+      <div data-testid="child" ref={ref}>
+        {isSideNavExpanded ? 'Expanded' : 'Collapsed'}
+      </div>
+    ));
+    render(
+      <SideNav aria-label="test" expanded>
+        <TestChild />
+      </SideNav>
+    );
+    expect(screen.getByTestId('child')).toHaveTextContent('Collapsed');
+  });
+
+  it('should not pass isSideNavExpanded to non-CarbsideNav children', () => {
+    const NonCarbonChild = () => <div data-testid="non-carbon-child" />;
+    render(
+      <SideNav aria-label="test" expanded>
+        <NonCarbonChild />
+      </SideNav>
+    );
+    expect(screen.getByTestId('non-carbon-child')).toBeInTheDocument();
+  });
+
+  it('should pass isSideNavExpanded correctly based on controlled state', () => {
+    const TestChild = React.forwardRef(({ isSideNavExpanded }, ref) => (
+      <div data-testid="child" ref={ref}>
+        {isSideNavExpanded ? 'Expanded' : 'Collapsed'}
+      </div>
+    ));
+    const { rerender } = render(
+      <SideNav aria-label="test" expanded>
+        <TestChild />
+      </SideNav>
+    );
+    expect(screen.getByTestId('child')).toHaveTextContent('Collapsed');
+    rerender(
+      <SideNav aria-label="test">
+        <TestChild />
+      </SideNav>
+    );
+    expect(screen.getByTestId('child')).toHaveTextContent('Collapsed');
+  });
+
+  it('should call handleToggle and onSideNavBlur when blurred', () => {
+    const onSideNavBlurMock = jest.fn();
+    const TestChild = () => <div data-testid="child">Child</div>;
+    const { getByRole } = render(
+      <SideNav aria-label="test" onSideNavBlur={onSideNavBlurMock}>
+        <TestChild />
+      </SideNav>
+    );
+    const sideNav = getByRole('navigation');
+    fireEvent.focus(sideNav);
+    fireEvent.blur(sideNav);
+    expect(onSideNavBlurMock).not.toHaveBeenCalled();
+  });
+
+  it('should not call onSideNavBlur if not expanded and isFixedNav is true', () => {
+    const onSideNavBlurMock = jest.fn();
+    const TestChild = () => <div data-testid="child">Child</div>;
+    const { getByRole } = render(
+      <SideNav aria-label="test" isFixedNav onSideNavBlur={onSideNavBlurMock}>
+        <TestChild />
+      </SideNav>
+    );
+    const sideNav = getByRole('navigation');
+    fireEvent.focus(sideNav);
+    fireEvent.blur(sideNav);
+    expect(onSideNavBlurMock).not.toHaveBeenCalled();
+  });
+
+  it('should call onSideNavBlur when blurred, is not fixed, and is expanded', () => {
+    const onSideNavBlurMock = jest.fn();
+    const TestChild = () => <div data-testid="child">Child</div>;
+    const { getByRole } = render(
+      <SideNav
+        aria-label="test"
+        onSideNavBlur={onSideNavBlurMock}
+        defaultExpanded>
+        <TestChild />
+      </SideNav>
+    );
+    const sideNav = getByRole('navigation');
+    fireEvent.focus(sideNav);
+    const unrelatedElement = document.createElement('div');
+    document.body.appendChild(unrelatedElement);
+    fireEvent.blur(sideNav, { relatedTarget: unrelatedElement });
+    expect(onSideNavBlurMock).toHaveBeenCalled();
+    document.body.removeChild(unrelatedElement);
+  });
+
+  it('should not call onSideNavBlur when isFixedNav is true', () => {
+    const onSideNavBlurMock = jest.fn();
+    const TestChild = () => <div data-testid="child">Child</div>;
+    const { getByRole } = render(
+      <SideNav
+        aria-label="test"
+        isFixedNav
+        onSideNavBlur={onSideNavBlurMock}
+        defaultExpanded>
+        <TestChild />
+      </SideNav>
+    );
+    const sideNav = getByRole('navigation');
+    fireEvent.focus(sideNav);
+    const unrelatedElement = document.createElement('div');
+    document.body.appendChild(unrelatedElement);
+    fireEvent.blur(sideNav, { relatedTarget: unrelatedElement });
+    expect(onSideNavBlurMock).not.toHaveBeenCalled();
+    document.body.removeChild(unrelatedElement);
+  });
+
+  it('should set expanded state to false on mouse leave', () => {
+    const onToggleMock = jest.fn();
+    const TestChild = () => <div data-testid="child">Child</div>;
+    const { getByRole } = render(
+      <SideNav aria-label="test" defaultExpanded onToggle={onToggleMock}>
+        <TestChild />
+      </SideNav>
+    );
+    const sideNav = getByRole('navigation');
+    expect(sideNav).toHaveClass('cds--side-nav__navigation');
+    fireEvent.mouseLeave(sideNav);
+    expect(sideNav).toHaveClass('cds--side-nav__navigation');
+  });
+
+  it('should handleToggle if isRail is true', () => {
+    const onToggleMock = jest.fn();
+    const TestChild = () => <div data-testid="child">Child</div>;
+    const { getByRole } = render(
+      <SideNav aria-label="test" onToggle={onToggleMock} isRail>
+        <TestChild />
+      </SideNav>
+    );
+    const sideNav = getByRole('navigation');
+    fireEvent.focus(sideNav);
+    expect(onToggleMock).toHaveBeenCalled();
+    fireEvent.mouseLeave(sideNav);
+    expect(onToggleMock).toHaveBeenCalledWith(false, false);
+    fireEvent.mouseEnter(sideNav);
+    expect(onToggleMock).toHaveBeenCalledWith(true, true);
+  });
+
+  it('should not call handleToggle if isRail is false', () => {
+    const onToggleMock = jest.fn();
+    const TestChild = () => <div data-testid="child">Child</div>;
+    const { getByRole } = render(
+      <SideNav
+        aria-label="test"
+        defaultExpanded
+        onToggle={onToggleMock}
+        isRail={false}>
+        <TestChild />
+      </SideNav>
+    );
+    const sideNav = getByRole('navigation');
+    fireEvent.mouseLeave(sideNav);
+    expect(onToggleMock).not.toHaveBeenCalled();
+  });
+
+  it('should expand the SideNav immediately on click', () => {
+    const TestChild = () => <div data-testid="child">Child</div>;
+    const onToggleMock = jest.fn();
+    const { getByRole } = render(
+      <SideNav aria-label="test" onToggle={onToggleMock} isRail>
+        <TestChild />
+      </SideNav>
+    );
+    const sideNav = getByRole('navigation');
+    expect(sideNav).not.toHaveClass('cds--side-nav--expanded');
+    fireEvent.click(sideNav);
+    expect(onToggleMock).toHaveBeenCalledWith(true, true);
+    expect(sideNav).toHaveClass('cds--side-nav--expanded');
+  });
+
+  it('should focus SideNav after tabbing from headerMenuButton', () => {
+    render(
+      <>
+        <button className="cds--header__menu-toggle"></button>
+        <SideNav
+          aria-label="test"
+          expanded
+          isFixedNav={false}
+          defaultExpanded
+        />
+      </>
+    );
+    const mockHeaderMenuButton = screen.getByRole('button');
+    const sideNav = screen.getByRole('navigation');
+
+    mockHeaderMenuButton.focus();
+    fireEvent.keyDown(window, { key: 'Tab' });
+    expect(document.activeElement).toBe(sideNav);
+  });
 });