diff --git a/packages/tailwindcss/src/config.ts b/packages/tailwindcss/src/config.ts
new file mode 100644
index 000000000..74d56ff7d
--- /dev/null
+++ b/packages/tailwindcss/src/config.ts
@@ -0,0 +1,26 @@
+import type { Plugin } from './plugins'
+
+export interface UserConfig {
+  /**
+   * A list of registered plugins
+   */
+  plugins?: Plugin[]
+}
+
+export interface ResolvedConfig {
+  /**
+   * A list of registered plugins
+   */
+  plugins: Plugin[]
+}
+
+export function resolve(config: UserConfig) {
+  let defaults: ResolvedConfig = {
+    plugins: [],
+  }
+
+  return {
+    ...defaults,
+    ...config,
+  }
+}
diff --git a/packages/tailwindcss/src/design-system.ts b/packages/tailwindcss/src/design-system.ts
index bebd82a33..dcfe13861 100644
--- a/packages/tailwindcss/src/design-system.ts
+++ b/packages/tailwindcss/src/design-system.ts
@@ -1,7 +1,9 @@
 import { toCss } from './ast'
 import { parseCandidate, parseVariant } from './candidate'
 import { compileAstNodes, compileCandidates } from './compile'
+import type { ResolvedConfig } from './config'
 import { getClassList, getVariants, type ClassEntry, type VariantEntry } from './intellisense'
+import { registerPlugins, type Plugin } from './plugins'
 import { getClassOrder } from './sort'
 import type { Theme } from './theme'
 import { Utilities, createUtilities } from './utilities'
@@ -12,6 +14,7 @@ export type DesignSystem = {
   theme: Theme
   utilities: Utilities
   variants: Variants
+  plugins: Plugin[]
 
   candidatesToCss(classes: string[]): (string | null)[]
   getClassOrder(classes: string[]): [string, bigint | null][]
@@ -25,7 +28,7 @@ export type DesignSystem = {
   getUsedVariants(): ReturnType<typeof parseVariant>[]
 }
 
-export function buildDesignSystem(theme: Theme): DesignSystem {
+export function buildDesignSystem(theme: Theme, config: ResolvedConfig): DesignSystem {
   let utilities = createUtilities(theme)
   let variants = createVariants(theme)
 
@@ -37,6 +40,7 @@ export function buildDesignSystem(theme: Theme): DesignSystem {
     theme,
     utilities,
     variants,
+    plugins: config.plugins,
 
     candidatesToCss(classes: string[]) {
       let result: (string | null)[] = []
@@ -77,5 +81,7 @@ export function buildDesignSystem(theme: Theme): DesignSystem {
     },
   }
 
+  registerPlugins(designSystem)
+
   return designSystem
 }
diff --git a/packages/tailwindcss/src/index.ts b/packages/tailwindcss/src/index.ts
index 34a095584..8817c5de7 100644
--- a/packages/tailwindcss/src/index.ts
+++ b/packages/tailwindcss/src/index.ts
@@ -1,13 +1,21 @@
 import { version } from '../package.json'
 import { WalkAction, comment, decl, rule, toCss, walk, type AstNode, type Rule } from './ast'
 import { compileCandidates } from './compile'
+import { resolve, type UserConfig } from './config'
 import * as CSS from './css-parser'
 import { buildDesignSystem } from './design-system'
 import { Theme } from './theme'
 
-export function compile(css: string): {
+export function compile(
+  css: string,
+  config?: UserConfig,
+): {
   build(candidates: string[]): string
+  readonly plugins: string[]
 } {
+  let resolved = resolve(config ?? {})
+  let plugins: string[] = []
+
   let ast = CSS.parse(css)
 
   if (process.env.NODE_ENV !== 'test') {
@@ -47,6 +55,20 @@ export function compile(css: string): {
       replaceWith(node.nodes)
     }
 
+    if (node.selector.startsWith('@plugin')) {
+      let path = node.selector
+        // Ignore `@plugin` when parsing the selector
+        .slice(7)
+        // Remove any surrounding spaces
+        .trim()
+        // Remove the surrounding quotes
+        .slice(1, -1)
+
+      plugins.push(path)
+      replaceWith([])
+      return WalkAction.Skip
+    }
+
     if (node.selector !== '@theme' && node.selector !== '@theme reference') return
 
     let isReference = node.selector === '@theme reference'
@@ -125,7 +147,7 @@ export function compile(css: string): {
     firstThemeRule.nodes = nodes
   }
 
-  let designSystem = buildDesignSystem(theme)
+  let designSystem = buildDesignSystem(theme, resolved)
 
   let tailwindUtilitiesNode: Rule | null = null
 
@@ -188,6 +210,7 @@ export function compile(css: string): {
   let previousAstNodeCount = 0
 
   return {
+    plugins,
     build(newRawCandidates: string[]) {
       let didChange = false
 
@@ -248,5 +271,5 @@ export function __unstable__loadDesignSystem(css: string) {
     })
   })
 
-  return buildDesignSystem(theme)
+  return buildDesignSystem(theme, resolve({}))
 }
diff --git a/packages/tailwindcss/src/plugins.test.ts b/packages/tailwindcss/src/plugins.test.ts
new file mode 100644
index 000000000..b8662db8c
--- /dev/null
+++ b/packages/tailwindcss/src/plugins.test.ts
@@ -0,0 +1,177 @@
+import { test, vi } from 'vitest'
+import { compile } from '.'
+import type { UserConfig } from './config'
+import type { Plugin } from './plugins'
+import { compileWithPlugins, run } from './test-utils/run'
+
+const css = String.raw
+
+test('Plugins are called', ({ expect }) => {
+  let fn = vi.fn()
+  let handler = vi.fn()
+  let config: UserConfig = {
+    plugins: [fn, { handler }],
+  }
+
+  run([], config)
+
+  expect(fn).toHaveBeenCalledWith(
+    expect.objectContaining({
+      addUtility: expect.any(Function),
+      addUtilities: expect.any(Function),
+      addVariant: expect.any(Function),
+      addVariants: expect.any(Function),
+    }),
+  )
+
+  expect(handler).toHaveBeenCalledWith(
+    expect.objectContaining({
+      addUtility: expect.any(Function),
+      addUtilities: expect.any(Function),
+      addVariant: expect.any(Function),
+      addVariants: expect.any(Function),
+    }),
+  )
+})
+
+test('Asynchronous plugins are waited on', async ({ expect }) => {
+  let before = vi.fn()
+  let after = vi.fn()
+  let config: UserConfig = {
+    plugins: [
+      async () => {
+        before()
+        await new Promise((resolve) => setTimeout(resolve))
+        after()
+      },
+    ],
+  }
+
+  await run([], config)
+
+  expect(before).toHaveBeenCalled()
+  expect(after).toHaveBeenCalled()
+})
+
+test('Custom static utilities', ({ expect }) => {
+  let config: UserConfig = {
+    plugins: [
+      ({ addUtilities }) => {
+        addUtilities({
+          '.my-red': {
+            color: 'red',
+            '& > *': {
+              color: 'lightred',
+            },
+          },
+          '.my-blue': {
+            color: 'red',
+          },
+        })
+      },
+    ],
+  }
+
+  expect(run(['my-red'], config)).toMatchInlineSnapshot(`
+    ".my-red {
+      color: red;
+    }"
+  `)
+  expect(run(['-my-red', 'my-red-[--value]'], config)).toEqual('')
+})
+
+test('Custom functional utilities', ({ expect }) => {
+  let config: UserConfig = {
+    plugins: [
+      ({ addUtilities }) => {
+        addUtilities({
+          '.my-fn': (value, { modifier }) => ({
+            color: modifier ? `${value ?? ''} / ${modifier ?? ''}` : `${value ?? ''}`,
+          }),
+        })
+      },
+    ],
+  }
+
+  expect(run(['my-fn', 'my-fn-[--value]', 'my-fn-[--value]/25'], config)).toMatchInlineSnapshot(`
+    ".my-fn {
+      color: ;
+    }
+
+    .my-fn-\\[--value\\] {
+      color: var(--value);
+    }
+
+    .my-fn-\\[--value\\]\\/25 {
+      color: var(--value) / 25;
+    }"
+  `)
+})
+
+test('Custom static variants', ({ expect }) => {
+  let config: UserConfig = {
+    plugins: [
+      ({ addVariant }) => {
+        addVariant('hocus', ['&:hover', '&:focus'])
+        addVariant('hactive', ['&:hover', '&:active'])
+      },
+    ],
+  }
+
+  expect(run(['hocus:underline'], config)).toMatchInlineSnapshot(`
+    ".hocus\\:underline:hover, .hocus\\:underline:focus {
+      text-decoration-line: underline;
+    }"
+  `)
+  expect(run(['hover/foo:underline', 'hover-[123]:underline'], config)).toEqual('')
+})
+
+test('Custom functional variants', ({ expect }) => {
+  let config: UserConfig = {
+    plugins: [
+      ({ addVariant }) => {
+        addVariant('in', ({ value, modifier }) => {
+          return modifier ? [] : value ? `&:is(${value} *)` : []
+        })
+      },
+    ],
+  }
+
+  expect(run(['in-[:checked]:underline'], config)).toMatchInlineSnapshot(`
+    ".in-\\[\\:checked\\]\\:underline:is(:checked *) {
+      text-decoration-line: underline;
+    }"
+  `)
+  expect(run(['in-[:checked]/foo:underline'], config)).toEqual('')
+})
+
+test('Plugins registered in CSS can be returned', ({ expect }) => {
+  let builder = compile(css`
+    @plugin "my-plugin";
+    @plugin "./my-plugin";
+  `)
+
+  expect(builder.plugins).toEqual(['my-plugin', './my-plugin'])
+})
+
+test.only('Plugins registered in CSS can be used', async ({ expect }) => {
+  vi.doMock('my-plugin', () => {
+    let plugin: Plugin = ({ addVariant }) => {
+      addVariant('hocus', ['&:hover', '&:focus'])
+    }
+
+    return {
+      default: plugin,
+    }
+  })
+
+  let result = await compileWithPlugins('@plugin "my-plugin"; @tailwind utilities;', [
+    'hocus:underline',
+  ])
+
+  expect(result).toMatchInlineSnapshot(`
+    ".hocus\\:underline:hover, .hocus\\:underline:focus {
+      text-decoration-line: underline;
+    }"
+  `)
+})
diff --git a/packages/tailwindcss/src/plugins.ts b/packages/tailwindcss/src/plugins.ts
new file mode 100644
index 000000000..ce06ed16a
--- /dev/null
+++ b/packages/tailwindcss/src/plugins.ts
@@ -0,0 +1,169 @@
+import { decl, rule, type AstNode, type Rule } from './ast'
+import type { Candidate } from './candidate'
+import type { DesignSystem } from './design-system'
+
+export type MatchData = {
+  value: string | null
+  modifier: string | null
+}
+
+export type SelectorFormat = CssSelectors | ((candidate: MatchData) => CssSelectors)
+export type UtilityFormat = CssTree | ((value: string | null, candidate: MatchData) => CssTree)
+
+export type CssSelectors = string | string[]
+export interface CssTree extends Record<string, string | CssTree> {}
+
+export interface PluginAPI {
+  addVariant(name: string, format: SelectorFormat): void
+  addVariants(variants: Record<string, SelectorFormat>): void
+
+  addUtility(name: string, format: UtilityFormat): void
+  addUtilities(utilities: Record<string, UtilityFormat>): void
+}
+
+export type Plugin = FunctionalPlugin | ConfigurablePlugin
+
+export interface FunctionalPlugin {
+  (api: PluginAPI): void | Promise<void>
+}
+
+export interface ConfigurablePlugin {
+  handler(api: PluginAPI): void | Promise<void>
+}
+
+/**
+ * Convert a recursive object structure to an AST
+ * Leaf nodes are declarations and branches are rules
+ **/
+function treeToAst(props: CssTree): AstNode[] {
+  let ast: AstNode[] = []
+
+  for (let [name, value] of Object.entries(props)) {
+    if (typeof value === 'string') {
+      if (value.startsWith('@')) {
+        ast.push(rule(name, []))
+      } else {
+        ast.push(decl(name, value))
+      }
+    } else {
+      ast.push(rule(name, treeToAst(value)))
+    }
+  }
+
+  return ast
+}
+
+/**
+ * Convert a recursive object structure to an AST
+ * Leaf nodes are declarations and branches are rules
+ **/
+function selectorsToAst(r: Rule, selectors: CssSelectors): AstNode[] {
+  if (typeof selectors === 'string') {
+    return [rule(selectors, r.nodes)]
+  }
+
+  return selectors.map((selector) => rule(selector, r.nodes))
+}
+
+/**
+ * Convert a recursive object structure to an AST
+ * Leaf nodes are declarations and branches are rules
+ **/
+function utilityToAst(
+  candidate: Extract<Candidate, { kind: 'functional' | 'static' }>,
+  props: UtilityFormat,
+): AstNode[] {
+  if (candidate.kind === 'static') {
+    if (candidate.negative) {
+      return []
+    }
+
+    if (typeof props === 'object') {
+      return treeToAst(props)
+    }
+
+    return []
+  }
+
+  if (typeof props === 'object') {
+    return treeToAst(props)
+  }
+
+  let match = {
+    value: candidate.value?.value ?? null,
+    modifier: candidate.modifier?.value ?? null,
+  }
+
+  return treeToAst(props(match.value, match))
+}
+
+export function registerPlugins(design: DesignSystem) {
+  let { utilities, variants } = design
+
+  function addUtility(name: string, format: UtilityFormat) {
+    if (name.startsWith('.')) {
+      name = name.slice(1)
+    }
+
+    if (typeof format === 'object') {
+      utilities.static(name, (candidate) => utilityToAst(candidate, format))
+
+      return
+    }
+
+    utilities.functional(name, (candidate) => utilityToAst(candidate, format))
+  }
+
+  function addUtilities(list: Record<string, UtilityFormat>) {
+    for (let [className, format] of Object.entries(list)) {
+      addUtility(className, format)
+    }
+  }
+
+  function addVariant(name: string, format: SelectorFormat) {
+    if (typeof format === 'string' || Array.isArray(format)) {
+      variants.static(
+        name,
+        (r) => {
+          r.nodes = selectorsToAst(r, format)
+        },
+        { compounds: true },
+      )
+
+      return
+    }
+
+    variants.functional(
+      name,
+      (r, variant) => {
+        let match = {
+          value: variant.value?.value ?? null,
+          modifier: variant.modifier?.value ?? null,
+        }
+
+        let resolved = format(match)
+
+        r.nodes = selectorsToAst(r, resolved)
+      },
+      { compounds: true },
+    )
+  }
+
+  function addVariants(list: Record<string, SelectorFormat>) {
+    for (let [name, format] of Object.entries(list)) {
+      addVariant(name, format)
+    }
+  }
+
+  for (let plugin of design.plugins) {
+    let handler = typeof plugin === 'function' ? plugin : plugin.handler
+
+    handler({
+      // v3 compatible legacy API
+      addUtility,
+      addUtilities,
+      addVariant,
+      addVariants,
+    })
+  }
+}
diff --git a/packages/tailwindcss/src/test-utils/run.ts b/packages/tailwindcss/src/test-utils/run.ts
index d360f2eaa..af0cfea05 100644
--- a/packages/tailwindcss/src/test-utils/run.ts
+++ b/packages/tailwindcss/src/test-utils/run.ts
@@ -1,12 +1,30 @@
 import { Features, transform } from 'lightningcss'
 import { compile } from '..'
+import { type UserConfig } from '../config'
+import type { Plugin } from '../plugins'
 
-export function compileCss(css: string, candidates: string[] = []) {
-  return optimizeCss(compile(css).build(candidates)).trim()
+export function compileCss(css: string, candidates: string[] = [], config: UserConfig = {}) {
+  return optimizeCss(compile(css, config).build(candidates)).trim()
 }
 
-export function run(candidates: string[]) {
-  return optimizeCss(compile('@tailwind utilities;').build(candidates)).trim()
+export function run(candidates: string[], config: UserConfig = {}) {
+  return optimizeCss(compile('@tailwind utilities;', config).build(candidates)).trim()
+}
+
+export async function compileWithPlugins(
+  css: string,
+  candidates: string[],
+  config: UserConfig = {},
+) {
+  let builder = compile(css, config)
+
+  let plugins: Plugin[] = await Promise.all(
+    builder.plugins.map((pluginPath) => import(pluginPath).then((mod) => mod.default)),
+  )
+
+  config.plugins = [...(config.plugins ?? []), ...plugins]
+
+  return optimizeCss(builder.build(candidates)).trim()
 }
 
 export function optimizeCss(