diff --git a/src/context/WindowContext.tsx b/src/context/WindowContext.tsx
new file mode 100644
index 0000000..ea90cc1
--- /dev/null
+++ b/src/context/WindowContext.tsx
@@ -0,0 +1,166 @@
+import React, { createContext, useContext, useReducer, useCallback } from 'react';
+import type { OSState, OSAction, WindowState } from '../types';
+import { APPS } from '../config/apps';
+
+function initWindows(): Record<string, WindowState> {
+  const map: Record<string, WindowState> = {};
+  for (const app of APPS) {
+    map[app.id] = {
+      id: app.id,
+      isOpen: false,
+      isMinimized: false,
+      isMaximized: false,
+      zIndex: 1,
+      position: { ...app.defaultPosition },
+      size: { ...app.defaultSize },
+      prevPosition: { ...app.defaultPosition },
+      prevSize: { ...app.defaultSize },
+    };
+  }
+  return map;
+}
+
+const initialState: OSState = {
+  windows: initWindows(),
+  topZ: 10,
+  wallpaper: 0,
+};
+
+function reducer(state: OSState, action: OSAction): OSState {
+  switch (action.type) {
+    case 'OPEN': {
+      const newZ = state.topZ + 1;
+      return {
+        ...state,
+        topZ: newZ,
+        windows: {
+          ...state.windows,
+          [action.id]: {
+            ...state.windows[action.id],
+            isOpen: true,
+            isMinimized: false,
+            zIndex: newZ,
+          },
+        },
+      };
+    }
+    case 'CLOSE':
+      return {
+        ...state,
+        windows: {
+          ...state.windows,
+          [action.id]: { ...state.windows[action.id], isOpen: false, isMinimized: false, isMaximized: false },
+        },
+      };
+    case 'MINIMIZE':
+      return {
+        ...state,
+        windows: {
+          ...state.windows,
+          [action.id]: { ...state.windows[action.id], isMinimized: true },
+        },
+      };
+    case 'MAXIMIZE': {
+      const win = state.windows[action.id];
+      if (win.isMaximized) {
+        return {
+          ...state,
+          windows: {
+            ...state.windows,
+            [action.id]: {
+              ...win,
+              isMaximized: false,
+              position: { ...win.prevPosition },
+              size: { ...win.prevSize },
+            },
+          },
+        };
+      }
+      return {
+        ...state,
+        windows: {
+          ...state.windows,
+          [action.id]: {
+            ...win,
+            isMaximized: true,
+            prevPosition: { ...win.position },
+            prevSize: { ...win.size },
+            position: { x: 0, y: 28 }, // 28px = menubar height
+            // viewport dims passed in from caller — keeps reducer pure
+            size: { width: action.viewportWidth, height: action.viewportHeight - 28 - 72 },
+          },
+        },
+      };
+    }
+    case 'FOCUS': {
+      const newZ = state.topZ + 1;
+      return {
+        ...state,
+        topZ: newZ,
+        windows: {
+          ...state.windows,
+          [action.id]: { ...state.windows[action.id], zIndex: newZ, isMinimized: false },
+        },
+      };
+    }
+    case 'MOVE':
+      return {
+        ...state,
+        windows: {
+          ...state.windows,
+          [action.id]: { ...state.windows[action.id], position: { x: action.x, y: action.y } },
+        },
+      };
+    case 'RESIZE':
+      return {
+        ...state,
+        windows: {
+          ...state.windows,
+          [action.id]: { ...state.windows[action.id], size: { width: action.width, height: action.height } },
+        },
+      };
+    case 'SET_WALLPAPER':
+      return { ...state, wallpaper: action.index };
+    default:
+      return state;
+  }
+}
+
+interface WindowContextType {
+  state: OSState;
+  openWindow: (id: string) => void;
+  closeWindow: (id: string) => void;
+  minimizeWindow: (id: string) => void;
+  maximizeWindow: (id: string, viewportWidth: number, viewportHeight: number) => void;
+  focusWindow: (id: string) => void;
+  moveWindow: (id: string, x: number, y: number) => void;
+  resizeWindow: (id: string, width: number, height: number) => void;
+  setWallpaper: (index: number) => void;
+}
+
+const WindowContext = createContext<WindowContextType | null>(null);
+
+export function WindowProvider({ children }: { children: React.ReactNode }) {
+  const [state, dispatch] = useReducer(reducer, initialState);
+
+  const openWindow = useCallback((id: string) => dispatch({ type: 'OPEN', id }), []);
+  const closeWindow = useCallback((id: string) => dispatch({ type: 'CLOSE', id }), []);
+  const minimizeWindow = useCallback((id: string) => dispatch({ type: 'MINIMIZE', id }), []);
+  const maximizeWindow = useCallback((id: string, viewportWidth: number, viewportHeight: number) => dispatch({ type: 'MAXIMIZE', id, viewportWidth, viewportHeight }), []);
+  const focusWindow = useCallback((id: string) => dispatch({ type: 'FOCUS', id }), []);
+  const moveWindow = useCallback((id: string, x: number, y: number) => dispatch({ type: 'MOVE', id, x, y }), []);
+  const resizeWindow = useCallback((id: string, w: number, h: number) => dispatch({ type: 'RESIZE', id, width: w, height: h }), []);
+  const setWallpaper = useCallback((index: number) => dispatch({ type: 'SET_WALLPAPER', index }), []);
+
+  return (
+    <WindowContext.Provider value={{ state, openWindow, closeWindow, minimizeWindow, maximizeWindow, focusWindow, moveWindow, resizeWindow, setWallpaper }}>
+      {children}
+    </WindowContext.Provider>
+  );
+}
+
+export function useOS() {
+  const ctx = useContext(WindowContext);
+  if (!ctx) throw new Error('useOS must be used within WindowProvider');
+  return ctx;
+}