diff --git a/src/player/quickslots.ts b/src/player/quickslots.ts
new file mode 100644
index 0000000..a514c61
--- /dev/null
+++ b/src/player/quickslots.ts
@@ -0,0 +1,66 @@
+/**
+ * Quick Slots — 4 Hotkey Slots for Fast Item Access
+ *
+ * Keys 1-4 select active slot. Active slot determines
+ * what gets thrown (F) or used. Items are referenced
+ * by id from the inventory.
+ */
+
+/** Number of quick slots */
+export const SLOT_COUNT = 4;
+
+/**
+ * Quick slots manager.
+ * Stores item ids assigned to 4 slots (keys 1-4).
+ * Active slot determines current "equipped" item.
+ */
+export class QuickSlots {
+  private slots: (string | null)[] = new Array(SLOT_COUNT).fill(null);
+
+  /** Currently active slot index (0-3) */
+  activeIndex = 0;
+
+  /** Assign an item id to a slot (null to clear) */
+  assign(index: number, itemId: string | null): void {
+    if (index < 0 || index >= SLOT_COUNT) return;
+    this.slots[index] = itemId;
+  }
+
+  /** Get item id in a slot (null if empty) */
+  getSlot(index: number): string | null {
+    if (index < 0 || index >= SLOT_COUNT) return null;
+    return this.slots[index];
+  }
+
+  /** Get item id in the active slot */
+  getActive(): string | null {
+    return this.slots[this.activeIndex];
+  }
+
+  /** Set active slot index (clamped to valid range) */
+  setActive(index: number): void {
+    this.activeIndex = Math.max(0, Math.min(SLOT_COUNT - 1, index));
+  }
+
+  /** Get all slot contents as array */
+  getAll(): (string | null)[] {
+    return [...this.slots];
+  }
+
+  /**
+   * Auto-assign an item to the first empty slot.
+   * Returns slot index, or -1 if no empty slot or item already assigned.
+   */
+  autoAssign(itemId: string): number {
+    // Don't duplicate
+    if (this.slots.includes(itemId)) return -1;
+
+    for (let i = 0; i < SLOT_COUNT; i++) {
+      if (this.slots[i] === null) {
+        this.slots[i] = itemId;
+        return i;
+      }
+    }
+    return -1;
+  }
+}
diff --git a/src/scenes/GameScene.ts b/src/scenes/GameScene.ts
index 3835a4f..faae1ad 100644
--- a/src/scenes/GameScene.ts
+++ b/src/scenes/GameScene.ts
@@ -23,6 +23,7 @@ import {
   projectileSystem,
   type ProjectileData,
 } from '../player/projectile';
+import { QuickSlots } from '../player/quickslots';
 import type { InputState } from '../player/types';
 
 export class GameScene extends Phaser.Scene {
@@ -40,6 +41,7 @@ export class GameScene extends Phaser.Scene {
   private tileSize!: number;
   private resourceData!: Map<number, ResourceInfo>;
   private projectileData!: Map<number, ProjectileData>;
+  private quickSlots!: QuickSlots;
   private keys!: {
     W: Phaser.Input.Keyboard.Key;
     A: Phaser.Input.Keyboard.Key;
@@ -47,6 +49,10 @@ export class GameScene extends Phaser.Scene {
     D: Phaser.Input.Keyboard.Key;
     E: Phaser.Input.Keyboard.Key;
     F: Phaser.Input.Keyboard.Key;
+    ONE: Phaser.Input.Keyboard.Key;
+    TWO: Phaser.Input.Keyboard.Key;
+    THREE: Phaser.Input.Keyboard.Key;
+    FOUR: Phaser.Input.Keyboard.Key;
   };
 
   // Interaction feedback
@@ -89,6 +95,7 @@ export class GameScene extends Phaser.Scene {
     const spawnY = spawn?.y ?? (biome.mapHeight * biome.tileSize) / 2;
     this.playerEid = createPlayerEntity(this.gameWorld.world, spawnX, spawnY);
     this.inventory = new Inventory(500, 20);
+    this.quickSlots = new QuickSlots();
 
     // 7. Camera — follow player, zoom via scroll wheel
     const worldPixelW = biome.mapWidth * biome.tileSize;
@@ -113,6 +120,10 @@ export class GameScene extends Phaser.Scene {
       D: keyboard.addKey('D'),
       E: keyboard.addKey('E'),
       F: keyboard.addKey('F'),
+      ONE: keyboard.addKey(Phaser.Input.Keyboard.KeyCodes.ONE),
+      TWO: keyboard.addKey(Phaser.Input.Keyboard.KeyCodes.TWO),
+      THREE: keyboard.addKey(Phaser.Input.Keyboard.KeyCodes.THREE),
+      FOUR: keyboard.addKey(Phaser.Input.Keyboard.KeyCodes.FOUR),
     };
 
     // 9. Minimap
@@ -189,10 +200,22 @@ export class GameScene extends Phaser.Scene {
       this.gameWorld.world, justPressedE, this.inventory, this.resourceData,
     );
     if (interaction) {
+      // Auto-assign collected items to quick slots
+      if (interaction.type === 'collected' || interaction.type === 'depleted') {
+        if (interaction.itemId) {
+          this.quickSlots.autoAssign(interaction.itemId);
+        }
+      }
       this.showInteractionFeedback(interaction.type, interaction.itemId);
     }
 
-    // 8. Throw projectile (F key, debounced)
+    // 8. Quick slot selection (1-4 keys)
+    if (this.keys.ONE.isDown) this.quickSlots.setActive(0);
+    if (this.keys.TWO.isDown) this.quickSlots.setActive(1);
+    if (this.keys.THREE.isDown) this.quickSlots.setActive(2);
+    if (this.keys.FOUR.isDown) this.quickSlots.setActive(3);
+
+    // 9. Throw projectile (F key, debounced) — uses active quick slot
     const isFDown = this.keys.F.isDown;
     const justPressedF = isFDown && !this.wasFDown;
     this.wasFDown = isFDown;
@@ -231,17 +254,15 @@ export class GameScene extends Phaser.Scene {
     );
   }
 
-  /** Try to launch a projectile from the first inventory item toward mouse */
+  /** Try to launch a projectile from active quick slot toward mouse */
   private tryLaunchProjectile(): void {
-    const items = this.inventory.getItems();
-    if (items.length === 0) {
+    const itemId = this.quickSlots.getActive();
+    if (!itemId || !this.inventory.hasItem(itemId)) {
       this.showInteractionFeedback('nothing_nearby');
       return;
     }
 
-    // Use first item in inventory (quick slots will replace this in 4.6)
-    const item = items[0];
-    const removed = this.inventory.removeItem(item.id, 1);
+    const removed = this.inventory.removeItem(itemId, 1);
     if (removed === 0) return;
 
     // Get mouse world position for direction
@@ -256,10 +277,16 @@ export class GameScene extends Phaser.Scene {
       this.projectileData,
       px, py,
       worldPoint.x, worldPoint.y,
-      item.id,
+      itemId,
     );
 
-    this.showInteractionFeedback('collected', `Threw ${item.id}`);
+    // Clear quick slot if inventory is now empty for this item
+    if (!this.inventory.hasItem(itemId)) {
+      const slotIdx = this.quickSlots.getAll().indexOf(itemId);
+      if (slotIdx >= 0) this.quickSlots.assign(slotIdx, null);
+    }
+
+    this.showInteractionFeedback('collected', `Threw ${itemId}`);
   }
 
   private showInteractionFeedback(type: string, itemId?: string): void {
diff --git a/tests/quickslots.test.ts b/tests/quickslots.test.ts
new file mode 100644
index 0000000..491f2f8
--- /dev/null
+++ b/tests/quickslots.test.ts
@@ -0,0 +1,131 @@
+/**
+ * Quick Slots Tests — Phase 4.6
+ *
+ * Tests: slot assignment, active selection, key switching.
+ */
+
+import { describe, it, expect } from 'vitest';
+import { QuickSlots, SLOT_COUNT } from '../src/player/quickslots';
+
+describe('QuickSlots — creation', () => {
+  it('starts with all slots empty', () => {
+    const qs = new QuickSlots();
+    for (let i = 0; i < SLOT_COUNT; i++) {
+      expect(qs.getSlot(i)).toBeNull();
+    }
+  });
+
+  it('starts with slot 0 active', () => {
+    const qs = new QuickSlots();
+    expect(qs.activeIndex).toBe(0);
+  });
+
+  it('has 4 slots', () => {
+    expect(SLOT_COUNT).toBe(4);
+    const qs = new QuickSlots();
+    expect(qs.getAll()).toHaveLength(4);
+  });
+});
+
+describe('QuickSlots — assignment', () => {
+  it('assigns item to slot', () => {
+    const qs = new QuickSlots();
+    qs.assign(0, 'Na');
+    expect(qs.getSlot(0)).toBe('Na');
+  });
+
+  it('replaces existing item in slot', () => {
+    const qs = new QuickSlots();
+    qs.assign(0, 'Na');
+    qs.assign(0, 'Fe');
+    expect(qs.getSlot(0)).toBe('Fe');
+  });
+
+  it('clears slot with null', () => {
+    const qs = new QuickSlots();
+    qs.assign(0, 'Na');
+    qs.assign(0, null);
+    expect(qs.getSlot(0)).toBeNull();
+  });
+
+  it('ignores invalid index', () => {
+    const qs = new QuickSlots();
+    qs.assign(-1, 'Na');
+    qs.assign(4, 'Na');
+    // No crash, no change
+    expect(qs.getAll()).toEqual([null, null, null, null]);
+  });
+});
+
+describe('QuickSlots — active slot', () => {
+  it('returns active slot item', () => {
+    const qs = new QuickSlots();
+    qs.assign(0, 'Na');
+    expect(qs.getActive()).toBe('Na');
+  });
+
+  it('returns null for empty active slot', () => {
+    const qs = new QuickSlots();
+    expect(qs.getActive()).toBeNull();
+  });
+
+  it('switches active slot', () => {
+    const qs = new QuickSlots();
+    qs.assign(0, 'Na');
+    qs.assign(1, 'Fe');
+    qs.assign(2, 'Cu');
+
+    qs.setActive(1);
+    expect(qs.activeIndex).toBe(1);
+    expect(qs.getActive()).toBe('Fe');
+
+    qs.setActive(2);
+    expect(qs.getActive()).toBe('Cu');
+  });
+
+  it('clamps active index to valid range', () => {
+    const qs = new QuickSlots();
+    qs.setActive(-1);
+    expect(qs.activeIndex).toBe(0);
+
+    qs.setActive(10);
+    expect(qs.activeIndex).toBe(3);
+  });
+});
+
+describe('QuickSlots — getAll', () => {
+  it('returns snapshot of all slots', () => {
+    const qs = new QuickSlots();
+    qs.assign(0, 'Na');
+    qs.assign(2, 'Fe');
+    expect(qs.getAll()).toEqual(['Na', null, 'Fe', null]);
+  });
+});
+
+describe('QuickSlots — auto-assign', () => {
+  it('assigns to first empty slot', () => {
+    const qs = new QuickSlots();
+    qs.assign(0, 'Na');
+    const index = qs.autoAssign('Fe');
+    expect(index).toBe(1);
+    expect(qs.getSlot(1)).toBe('Fe');
+  });
+
+  it('returns -1 when all slots full', () => {
+    const qs = new QuickSlots();
+    qs.assign(0, 'Na');
+    qs.assign(1, 'Fe');
+    qs.assign(2, 'Cu');
+    qs.assign(3, 'S');
+    const index = qs.autoAssign('H');
+    expect(index).toBe(-1);
+  });
+
+  it('does not duplicate item already in a slot', () => {
+    const qs = new QuickSlots();
+    qs.assign(0, 'Na');
+    const index = qs.autoAssign('Na');
+    expect(index).toBe(-1); // already assigned
+    expect(qs.getAll().filter(s => s === 'Na')).toHaveLength(1);
+  });
+});