diff --git a/babel.config.js b/babel.config.js
index 901553e56969..4b9c46dc91c7 100644
--- a/babel.config.js
+++ b/babel.config.js
@@ -34,7 +34,7 @@ const productionPlugins = [
 ];
 
 module.exports = function getBabelConfig(api) {
-  const useESModules = api.env(['legacy', 'modern', 'stable', 'rollup']);
+  const useESModules = api.env(['modern', 'stable', 'rollup']);
 
   const presets = [
     [
@@ -155,12 +155,6 @@ module.exports = function getBabelConfig(api) {
           ],
         ],
       },
-      legacy: {
-        plugins: [
-          // IE11 support
-          '@babel/plugin-transform-object-assign',
-        ],
-      },
       test: {
         sourceMaps: 'both',
         plugins: [
diff --git a/docs/babel.config.js b/docs/babel.config.js
index 2ec7799d6159..d7a30a01f913 100644
--- a/docs/babel.config.js
+++ b/docs/babel.config.js
@@ -35,8 +35,6 @@ module.exports = function getBabelConfig(api) {
     ],
     plugins: [
       ...baseConfig.plugins,
-      // for IE 11 support
-      '@babel/plugin-transform-object-assign',
       'babel-plugin-preval',
       [
         'babel-plugin-module-resolver',
diff --git a/docs/package.json b/docs/package.json
index f77536ef5970..a26ff9724e01 100644
--- a/docs/package.json
+++ b/docs/package.json
@@ -20,7 +20,6 @@
   },
   "dependencies": {
     "@babel/core": "^7.23.9",
-    "@babel/plugin-transform-object-assign": "^7.23.3",
     "@babel/runtime-corejs2": "^7.23.9",
     "@docsearch/react": "^3.5.2",
     "@emotion/cache": "^11.11.0",
diff --git a/package.json b/package.json
index ee0a6c2e5890..b26c3af51507 100644
--- a/package.json
+++ b/package.json
@@ -71,7 +71,6 @@
     "@babel/plugin-proposal-object-rest-spread": "^7.20.7",
     "@babel/plugin-proposal-private-methods": "^7.18.6",
     "@babel/plugin-proposal-private-property-in-object": "^7.21.11",
-    "@babel/plugin-transform-object-assign": "^7.23.3",
     "@babel/plugin-transform-react-constant-elements": "^7.23.3",
     "@babel/plugin-transform-runtime": "^7.23.9",
     "@babel/preset-env": "^7.23.9",
diff --git a/packages/x-charts/package.json b/packages/x-charts/package.json
index c22a7fd9789a..72aa4e026817 100644
--- a/packages/x-charts/package.json
+++ b/packages/x-charts/package.json
@@ -24,8 +24,7 @@
   ],
   "scripts": {
     "typescript": "tsc -p tsconfig.json",
-    "build": "yarn build:legacy && yarn build:modern && yarn build:node && yarn build:stable && yarn build:types && yarn build:copy-files ",
-    "build:legacy": "node ../../scripts/build.mjs legacy",
+    "build": "yarn build:modern && yarn build:node && yarn build:stable && yarn build:types && yarn build:copy-files ",
     "build:modern": "node ../../scripts/build.mjs modern",
     "build:node": "node ../../scripts/build.mjs node",
     "build:stable": "node ../../scripts/build.mjs stable",
diff --git a/packages/x-data-grid-generator/package.json b/packages/x-data-grid-generator/package.json
index 3a7ba6caf984..c0d6fbb6191e 100644
--- a/packages/x-data-grid-generator/package.json
+++ b/packages/x-data-grid-generator/package.json
@@ -18,8 +18,7 @@
   ],
   "scripts": {
     "typescript": "tsc -p tsconfig.json",
-    "build": "yarn build:legacy && yarn build:modern && yarn build:node && yarn build:stable && yarn build:types && yarn build:copy-files ",
-    "build:legacy": "node ../../scripts/build.mjs legacy",
+    "build": "yarn build:modern && yarn build:node && yarn build:stable && yarn build:types && yarn build:copy-files ",
     "build:modern": "node ../../scripts/build.mjs modern",
     "build:node": "node ../../scripts/build.mjs node",
     "build:stable": "node ../../scripts/build.mjs stable",
diff --git a/packages/x-data-grid-premium/package.json b/packages/x-data-grid-premium/package.json
index 257be83eff30..29876089f398 100644
--- a/packages/x-data-grid-premium/package.json
+++ b/packages/x-data-grid-premium/package.json
@@ -28,8 +28,7 @@
   ],
   "scripts": {
     "typescript": "tsc -p tsconfig.json",
-    "build": "yarn build:legacy && yarn build:modern && yarn build:node && yarn build:stable && yarn build:types && yarn build:copy-files ",
-    "build:legacy": "node ../../scripts/build.mjs legacy",
+    "build": "yarn build:modern && yarn build:node && yarn build:stable && yarn build:types && yarn build:copy-files ",
     "build:modern": "node ../../scripts/build.mjs modern",
     "build:node": "node ../../scripts/build.mjs node",
     "build:stable": "node ../../scripts/build.mjs stable",
diff --git a/packages/x-data-grid-pro/package.json b/packages/x-data-grid-pro/package.json
index d24f43d1e567..393f269df019 100644
--- a/packages/x-data-grid-pro/package.json
+++ b/packages/x-data-grid-pro/package.json
@@ -28,8 +28,7 @@
   ],
   "scripts": {
     "typescript": "tsc -p tsconfig.json",
-    "build": "yarn build:legacy && yarn build:modern && yarn build:node && yarn build:stable && yarn build:types && yarn build:copy-files ",
-    "build:legacy": "node ../../scripts/build.mjs legacy",
+    "build": "yarn build:modern && yarn build:node && yarn build:stable && yarn build:types && yarn build:copy-files ",
     "build:modern": "node ../../scripts/build.mjs modern",
     "build:node": "node ../../scripts/build.mjs node",
     "build:stable": "node ../../scripts/build.mjs stable",
diff --git a/packages/x-data-grid/package.json b/packages/x-data-grid/package.json
index 0d953341c1e2..be00018e31ad 100644
--- a/packages/x-data-grid/package.json
+++ b/packages/x-data-grid/package.json
@@ -32,8 +32,7 @@
   ],
   "scripts": {
     "typescript": "tsc -p tsconfig.json",
-    "build": "yarn build:legacy && yarn build:modern && yarn build:node && yarn build:stable && yarn build:types && yarn build:copy-files ",
-    "build:legacy": "node ../../scripts/build.mjs legacy",
+    "build": "yarn build:modern && yarn build:node && yarn build:stable && yarn build:types && yarn build:copy-files ",
     "build:modern": "node ../../scripts/build.mjs modern",
     "build:node": "node ../../scripts/build.mjs node",
     "build:stable": "node ../../scripts/build.mjs stable",
diff --git a/packages/x-date-pickers-pro/package.json b/packages/x-date-pickers-pro/package.json
index 81db8f8615e4..b16035fd3044 100644
--- a/packages/x-date-pickers-pro/package.json
+++ b/packages/x-date-pickers-pro/package.json
@@ -27,8 +27,7 @@
   ],
   "scripts": {
     "typescript": "tsc -p tsconfig.json",
-    "build": "yarn build:legacy && yarn build:modern && yarn build:node && yarn build:stable && yarn build:types && yarn build:copy-files ",
-    "build:legacy": "node ../../scripts/build.mjs legacy",
+    "build": "yarn build:modern && yarn build:node && yarn build:stable && yarn build:types && yarn build:copy-files ",
     "build:modern": "node ../../scripts/build.mjs modern",
     "build:node": "node ../../scripts/build.mjs node",
     "build:stable": "node ../../scripts/build.mjs stable",
diff --git a/packages/x-date-pickers/package.json b/packages/x-date-pickers/package.json
index 43830912ecdb..d868a884b178 100644
--- a/packages/x-date-pickers/package.json
+++ b/packages/x-date-pickers/package.json
@@ -30,8 +30,7 @@
   ],
   "scripts": {
     "typescript": "tsc -p tsconfig.json",
-    "build": "yarn build:legacy && yarn build:modern && yarn build:node && yarn build:stable && yarn build:types && yarn build:copy-files ",
-    "build:legacy": "node ../../scripts/build.mjs legacy",
+    "build": "yarn build:modern && yarn build:node && yarn build:stable && yarn build:types && yarn build:copy-files ",
     "build:modern": "node ../../scripts/build.mjs modern",
     "build:node": "node ../../scripts/build.mjs node",
     "build:stable": "node ../../scripts/build.mjs stable",
diff --git a/packages/x-license/package.json b/packages/x-license/package.json
index 2248ae3669b2..a9100b80b1d9 100644
--- a/packages/x-license/package.json
+++ b/packages/x-license/package.json
@@ -11,7 +11,6 @@
   "homepage": "https://mui.com/x/introduction/licensing/",
   "sideEffects": [
     "./utils/licenseInfo.js",
-    "./legacy/utils/licenseInfo.js",
     "./modern/utils/licenseInfo.js",
     "./node/utils/licenseInfo.js"
   ],
@@ -20,8 +19,7 @@
   },
   "scripts": {
     "typescript": "tsc -p tsconfig.json",
-    "build": "yarn build:legacy && yarn build:modern && yarn build:node && yarn build:stable && yarn build:types && yarn build:copy-files ",
-    "build:legacy": "node ../../scripts/build.mjs legacy",
+    "build": "yarn build:modern && yarn build:node && yarn build:stable && yarn build:types && yarn build:copy-files ",
     "build:modern": "node ../../scripts/build.mjs modern",
     "build:node": "node ../../scripts/build.mjs node",
     "build:stable": "node ../../scripts/build.mjs stable",
diff --git a/packages/x-tree-view/package.json b/packages/x-tree-view/package.json
index 27bd804b2129..b6e88d590c98 100644
--- a/packages/x-tree-view/package.json
+++ b/packages/x-tree-view/package.json
@@ -28,8 +28,7 @@
   ],
   "scripts": {
     "typescript": "tsc -p tsconfig.json",
-    "build": "yarn build:legacy && yarn build:modern && yarn build:node && yarn build:stable && yarn build:types && yarn build:copy-files ",
-    "build:legacy": "node ../../scripts/build.mjs legacy",
+    "build": "yarn build:modern && yarn build:node && yarn build:stable && yarn build:types && yarn build:copy-files ",
     "build:modern": "node ../../scripts/build.mjs modern",
     "build:node": "node ../../scripts/build.mjs node",
     "build:stable": "node ../../scripts/build.mjs stable",
diff --git a/scripts/build.mjs b/scripts/build.mjs
index 98098d8f3827..d24001abf0f5 100644
--- a/scripts/build.mjs
+++ b/scripts/build.mjs
@@ -9,8 +9,6 @@ import { getWorkspaceRoot } from './utils.mjs';
 const exec = promisify(childProcess.exec);
 
 const validBundles = [
-  // legacy build using ES6 modules
-  'legacy',
   // modern build with a rolling target using ES6 modules
   'modern',
   // build for node using commonJS modules
@@ -67,7 +65,6 @@ async function run(argv) {
       node: topLevelPathImportsCanBePackages ? './node' : './',
       modern: './modern',
       stable: topLevelPathImportsCanBePackages ? './' : './esm',
-      legacy: './legacy',
     }[bundle],
   );
 
diff --git a/scripts/copyFiles.mjs b/scripts/copyFiles.mjs
index 6d0199ee1c6b..b4b88fac6dd3 100644
--- a/scripts/copyFiles.mjs
+++ b/scripts/copyFiles.mjs
@@ -33,7 +33,6 @@ async function addLicense(packageData) {
   await Promise.all(
     [
       './index.js',
-      './legacy/index.js',
       './modern/index.js',
       './node/index.js',
       './umd/material-ui.development.js',
diff --git a/yarn.lock b/yarn.lock
index f80f786be1cb..28e7efc06615 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -916,13 +916,6 @@
     "@babel/helper-plugin-utils" "^7.22.5"
     "@babel/plugin-syntax-numeric-separator" "^7.10.4"
 
-"@babel/plugin-transform-object-assign@^7.23.3":
-  version "7.23.3"
-  resolved "https://registry.yarnpkg.com/@babel/plugin-transform-object-assign/-/plugin-transform-object-assign-7.23.3.tgz#64177e8cf943460c7f0e1c410277546804f59625"
-  integrity sha512-TPJ6O7gVC2rlQH2hvQGRH273G1xdoloCj9Pc07Q7JbIZYDi+Sv5gaE2fu+r5E7qK4zyt6vj0FbZaZTRU5C3OMA==
-  dependencies:
-    "@babel/helper-plugin-utils" "^7.22.5"
-
 "@babel/plugin-transform-object-rest-spread@^7.23.4":
   version "7.23.4"
   resolved "https://registry.yarnpkg.com/@babel/plugin-transform-object-rest-spread/-/plugin-transform-object-rest-spread-7.23.4.tgz#2b9c2d26bf62710460bdc0d1730d4f1048361b83"