diff --git a/.changeset/old-boxes-clap.md b/.changeset/old-boxes-clap.md
new file mode 100644
index 00000000000..27abb9698ec
--- /dev/null
+++ b/.changeset/old-boxes-clap.md
@@ -0,0 +1,5 @@
+---
+"@primer/react": minor
+---
+
+feat(Details): Add summary subcomponent
diff --git a/packages/react/src/Details/Details.docs.json b/packages/react/src/Details/Details.docs.json
index 51e5275b585..0dff5c8d6da 100644
--- a/packages/react/src/Details/Details.docs.json
+++ b/packages/react/src/Details/Details.docs.json
@@ -11,5 +11,26 @@
       "type": "SystemStyleObject"
     }
   ],
-  "subcomponents": []
+  "subcomponents": [
+    {
+      "name": "Details.Summary",
+      "props": [
+        {
+          "name": "as",
+          "type": "React.ElementType<React.PropsWithChildren<any>>",
+          "defaultValue": "summary",
+          "required": false,
+          "description": "HTML element to render summary as."
+        },
+        {
+          "name": "children",
+          "type": "React.ReactNode"
+        },
+        {
+          "name": "sx",
+          "type": "SystemStyleObject"
+        }
+      ]
+    }
+  ]
 }
diff --git a/packages/react/src/Details/Details.stories.tsx b/packages/react/src/Details/Details.stories.tsx
index cdebdccce97..799fee5ac5e 100644
--- a/packages/react/src/Details/Details.stories.tsx
+++ b/packages/react/src/Details/Details.stories.tsx
@@ -12,7 +12,7 @@ export const Default: StoryFn<typeof Details> = () => {
   const {getDetailsProps} = useDetails({closeOnOutsideClick: true})
   return (
     <Details {...getDetailsProps()}>
-      <Button as="summary">See Details</Button>
+      <Details.Summary as={Button}>See Details</Details.Summary>
       This is some content
     </Details>
   )
diff --git a/packages/react/src/Details/Details.tsx b/packages/react/src/Details/Details.tsx
index d90f76a7e2a..927edb6091f 100644
--- a/packages/react/src/Details/Details.tsx
+++ b/packages/react/src/Details/Details.tsx
@@ -1,4 +1,4 @@
-import React, {type ComponentPropsWithoutRef, type ReactElement} from 'react'
+import React, {useEffect, useState, type ComponentPropsWithoutRef, type ReactElement} from 'react'
 import styled from 'styled-components'
 import type {SxProp} from '../sx'
 import sx from '../sx'
@@ -6,6 +6,7 @@ import {toggleStyledComponent} from '../internal/utils/toggleStyledComponent'
 import {useFeatureFlag} from '../FeatureFlags'
 import {clsx} from 'clsx'
 import classes from './Details.module.css'
+import {useMergedRefs} from '../internal/hooks/useMergedRefs'
 
 const CSS_MODULES_FEATURE_FLAG = 'primer_react_css_modules_team'
 
@@ -24,18 +25,76 @@ const StyledDetails = toggleStyledComponent(
   `,
 )
 
-const Details = React.forwardRef<HTMLDetailsElement, DetailsProps>(
-  ({className, children, ...rest}, ref): ReactElement => {
+const Root = React.forwardRef<HTMLDetailsElement, DetailsProps>(
+  ({className, children, ...rest}, forwardRef): ReactElement => {
     const enabled = useFeatureFlag(CSS_MODULES_FEATURE_FLAG)
+    const detailsRef = React.useRef<HTMLDetailsElement>(null)
+    const ref = useMergedRefs(forwardRef, detailsRef)
+    const [hasSummary, setHasSummary] = useState(false)
+
+    useEffect(() => {
+      const {current: details} = detailsRef
+      if (!details) {
+        return
+      }
+
+      const updateSummary = () => {
+        const summary = details.querySelector('summary:not([data-default-summary])')
+        setHasSummary(!!summary)
+      }
+
+      // Update summary on mount
+      updateSummary()
+
+      const observer = new MutationObserver(() => {
+        updateSummary()
+      })
+
+      observer.observe(details, {
+        childList: true,
+        subtree: true,
+      })
+
+      return () => {
+        observer.disconnect()
+      }
+    }, [])
+
     return (
       <StyledDetails className={clsx(className, {[classes.Details]: enabled})} {...rest} ref={ref}>
+        {/* Include default summary if summary is not provided */}
+        {!hasSummary && <Details.Summary data-default-summary>{'See Details'}</Details.Summary>}
         {children}
       </StyledDetails>
     )
   },
 )
 
-Details.displayName = 'Details'
+Root.displayName = 'Details'
+
+export type SummaryProps<As extends React.ElementType> = {
+  /**
+   * HTML element to render summary as.
+   */
+  as?: As
+  children?: React.ReactNode
+} & React.ComponentPropsWithoutRef<React.ElementType extends As ? As : 'summary'>
+
+function Summary<As extends React.ElementType>({as, children, ...props}: SummaryProps<As>) {
+  const Component = as ?? 'summary'
+  return (
+    <Component as={Component === 'summary' ? null : 'summary'} {...props}>
+      {children}
+    </Component>
+  )
+}
+Summary.displayName = 'Summary'
+
+export {Summary}
+
+const Details = Object.assign(Root, {
+  Summary,
+})
 
 export type DetailsProps = ComponentPropsWithoutRef<'details'> & SxProp
 export default Details
diff --git a/packages/react/src/Details/__tests__/Details.test.tsx b/packages/react/src/Details/__tests__/Details.test.tsx
index bac07624624..28be85e0945 100644
--- a/packages/react/src/Details/__tests__/Details.test.tsx
+++ b/packages/react/src/Details/__tests__/Details.test.tsx
@@ -1,6 +1,6 @@
-import {render} from '@testing-library/react'
+import {render, screen} from '@testing-library/react'
 import userEvent from '@testing-library/user-event'
-import React from 'react'
+import React, {act} from 'react'
 import {Details, useDetails, Box, Button} from '../..'
 import type {ButtonProps} from '../../Button'
 import {behavesAsComponent, checkExports} from '../../utils/testing'
@@ -14,29 +14,36 @@ describe('Details', () => {
   })
 
   it('should have no axe violations', async () => {
-    const {container} = render(<Details />)
-    const results = await axe.run(container)
+    const {container} = render(
+      <Details>
+        <Details.Summary>Summary</Details.Summary>Content
+      </Details>,
+    )
+    let results
+    await act(async () => {
+      results = await axe.run(container)
+    })
     expect(results).toHaveNoViolations()
   })
 
-  it('Toggles when you click outside', () => {
+  it('Toggles when you click outside', async () => {
     const Component = () => {
       const {getDetailsProps} = useDetails({closeOnOutsideClick: true})
       return (
         <Details data-testid="details" {...getDetailsProps()}>
-          <summary>hi</summary>
+          <Details.Summary>hi</Details.Summary>
         </Details>
       )
     }
 
-    const {getByTestId} = render(<Component />)
+    const {findByTestId} = render(<Component />)
 
     document.body.click()
 
-    expect(getByTestId('details')).not.toHaveAttribute('open')
+    expect(await findByTestId('details')).not.toHaveAttribute('open')
   })
 
-  it('Accurately passes down open state', () => {
+  it('Accurately passes down open state', async () => {
     const Component = () => {
       const {getDetailsProps, open} = useDetails({closeOnOutsideClick: true})
       return (
@@ -46,12 +53,12 @@ describe('Details', () => {
       )
     }
 
-    const {getByTestId} = render(<Component />)
+    const {findByTestId} = render(<Component />)
 
     document.body.click()
 
-    expect(getByTestId('summary')).toHaveTextContent('Closed')
-    expect(getByTestId('details')).not.toHaveAttribute('open')
+    expect(await findByTestId('summary')).toHaveTextContent('Closed')
+    expect(await findByTestId('details')).not.toHaveAttribute('open')
   })
 
   it('Can manipulate state with setOpen', async () => {
@@ -95,4 +102,53 @@ describe('Details', () => {
 
     expect(getByTestId('summary')).toHaveTextContent('Open')
   })
+
+  it('Adds default summary if no summary supplied', async () => {
+    const {getByText} = render(<Details data-testid="details">content</Details>)
+
+    expect(getByText('See Details')).toBeInTheDocument()
+    expect(getByText('See Details').tagName).toBe('SUMMARY')
+  })
+
+  it('Does not add default summary if summary supplied', async () => {
+    const {findByTestId, findByText} = render(
+      <Details data-testid="details">
+        <Details.Summary data-testid="summary">summary</Details.Summary>
+        content
+      </Details>,
+    )
+
+    await expect(findByText('See Details')).rejects.toThrow()
+    expect(await findByTestId('summary')).toBeInTheDocument()
+    expect((await findByTestId('summary')).tagName).toBe('SUMMARY')
+  })
+
+  it('Does not add default summary if supplied as different element', async () => {
+    const {findByTestId, findByText} = render(
+      <Details data-testid="details">
+        <Box as="summary" data-testid="summary">
+          custom summary
+        </Box>
+        content
+      </Details>,
+    )
+
+    await expect(findByText('See Details')).rejects.toThrow()
+    expect(await findByTestId('summary')).toBeInTheDocument()
+    expect((await findByTestId('summary')).tagName).toBe('SUMMARY')
+  })
+
+  describe('Details.Summary', () => {
+    behavesAsComponent({Component: Details.Summary, options: {skipSx: true}})
+
+    it('should support a custom `className` on the container element', () => {
+      render(<Details.Summary className="custom-class">test summary</Details.Summary>)
+      expect(screen.getByText('test summary')).toHaveClass('custom-class')
+    })
+
+    it('should pass extra props onto the container element', () => {
+      render(<Details.Summary data-testid="test">test summary</Details.Summary>)
+      expect(screen.getByText('test summary')).toHaveAttribute('data-testid', 'test')
+    })
+  })
 })