diff --git a/app/models/item.rb b/app/models/item.rb
index fef2ece7..e1b1c5db 100644
--- a/app/models/item.rb
+++ b/app/models/item.rb
@@ -549,6 +549,22 @@ class Item < ApplicationRecord
       return [] if empty?
       ([item] + swf_assets).map(&:restricted_zone_ids).flatten.uniq.sort
     end
+
+    # Check if this appearance is compatible with another appearance.
+    # Two appearances are incompatible if:
+    # 1. They occupy the same zone (can't wear two items in same slot)
+    # 2. One restricts a zone the other occupies (e.g., hat restricts hair zone)
+    def compatible_with?(other)
+      occupied = occupied_zone_ids
+      other_occupied = other.occupied_zone_ids
+      restricted = restricted_zone_ids
+      other_restricted = other.restricted_zone_ids
+
+      # Check for zone conflicts
+      (occupied & other_occupied).empty? &&
+        (restricted & other_occupied).empty? &&
+        (other_restricted & occupied).empty?
+    end
   end
   Appearance::Body = Struct.new(:id, :species) do
     include ActiveModel::Serializers::JSON
diff --git a/app/models/outfit.rb b/app/models/outfit.rb
index 8c4db97e..21138789 100644
--- a/app/models/outfit.rb
+++ b/app/models/outfit.rb
@@ -287,8 +287,8 @@ class Outfit < ApplicationRecord
   # associations.
   def dup
     super.tap do |outfit|
-      outfit.worn_item_ids = self.worn_item_ids
-      outfit.closeted_item_ids = self.closeted_item_ids
+      outfit.worn_items = self.worn_items
+      outfit.closeted_items = self.closeted_items
     end
   end
 
@@ -298,7 +298,38 @@ class Outfit < ApplicationRecord
   end
 
   # Create a copy of this outfit, additionally wearing the given item.
+  # Automatically moves any incompatible worn items to the closet.
   def with_item(item)
-    dup.tap { |o| o.worn_items << item unless o.worn_items.include?(item) }
+    dup.tap do |o|
+      # Skip if item is nil, already worn, or outfit has no pet_state
+      next if item.nil? || o.worn_item_ids.include?(item.id) || o.pet_state.nil?
+
+      # Load appearances for the new item and all currently worn items
+      all_items = o.worn_items + [item]
+      appearances = Item.appearances_for(all_items, o.pet_type,
+        swf_asset_includes: [:zone])
+
+      new_item_appearance = appearances[item.id]
+
+      # If the new item has no appearance (doesn't fit this pet), skip it
+      next if new_item_appearance.empty?
+
+      # Find items that conflict with the new item
+      conflicting_items = o.worn_items.select do |worn_item|
+        worn_appearance = appearances[worn_item.id]
+        # Empty appearances are always compatible
+        !worn_appearance.empty? &&
+          !new_item_appearance.compatible_with?(worn_appearance)
+      end
+
+      # Move conflicting items to closet
+      conflicting_items.each do |conflicting_item|
+        o.worn_items.delete(conflicting_item)
+        o.closeted_items << conflicting_item unless o.closeted_item_ids.include?(conflicting_item.id)
+      end
+
+      # Add the new item
+      o.worn_items << item
+    end
   end
 end
diff --git a/spec/models/outfit_spec.rb b/spec/models/outfit_spec.rb
new file mode 100644
index 00000000..b1a4758f
--- /dev/null
+++ b/spec/models/outfit_spec.rb
@@ -0,0 +1,288 @@
+require_relative '../rails_helper'
+
+RSpec.describe Outfit do
+	fixtures :colors, :species, :zones
+
+	let(:blue) { colors(:blue) }
+	let(:acara) { species(:acara) }
+
+	before do
+		PetType.destroy_all
+		@pet_type = PetType.create!(color: blue, species: acara, body_id: 1)
+		@pet_state = create_pet_state(@pet_type, "HAPPY_MASC")
+		@outfit = Outfit.new(pet_state: @pet_state)
+	end
+
+	def create_pet_state(pet_type, pose)
+		# Create a basic biology asset so pet state saves correctly
+		swf_asset = SwfAsset.create!(
+			type: "biology",
+			remote_id: (SwfAsset.maximum(:remote_id) || 0) + 1,
+			url: "https://images.neopets.example/biology.swf",
+			zone: zones(:body),
+			zones_restrict: "",
+			body_id: pet_type.body_id
+		)
+		PetState.create!(
+			pet_type: pet_type,
+			pose: pose,
+			swf_assets: [swf_asset],
+			swf_asset_ids: [swf_asset.id]
+		)
+	end
+
+	def create_item(name, zone, body_id: 1, zones_restrict: "")
+		item = Item.create!(
+			name: name,
+			description: "Test item",
+			thumbnail_url: "https://images.neopets.example/item.png",
+			zones_restrict: zones_restrict,
+			rarity: "Common",
+			price: 100
+		)
+		swf_asset = SwfAsset.create!(
+			type: "object",
+			remote_id: (SwfAsset.maximum(:remote_id) || 0) + 1,
+			url: "https://images.neopets.example/#{name}.swf",
+			zone: zone,
+			zones_restrict: zones_restrict,
+			body_id: body_id
+		)
+		item.swf_assets << swf_asset
+		item
+	end
+
+	describe "Item::Appearance#compatible_with?" do
+		it "returns true for items in different zones with no restrictions" do
+			hat = create_item("Hat", zones(:hat))
+			shirt = create_item("Shirt", zones(:shirtdress))
+
+			appearances = Item.appearances_for([hat, shirt], @pet_type)
+			hat_appearance = appearances[hat.id]
+			shirt_appearance = appearances[shirt.id]
+
+			expect(hat_appearance.compatible_with?(shirt_appearance)).to be true
+			expect(shirt_appearance.compatible_with?(hat_appearance)).to be true
+		end
+
+		it "returns false for items in the same zone" do
+			hat1 = create_item("Hat 1", zones(:hat))
+			hat2 = create_item("Hat 2", zones(:hat))
+
+			appearances = Item.appearances_for([hat1, hat2], @pet_type)
+			hat1_appearance = appearances[hat1.id]
+			hat2_appearance = appearances[hat2.id]
+
+			expect(hat1_appearance.compatible_with?(hat2_appearance)).to be false
+			expect(hat2_appearance.compatible_with?(hat1_appearance)).to be false
+		end
+
+		it "returns false when one item restricts a zone the other occupies" do
+			# Create a hat that restricts the ruff zone (zone 29)
+			# The zones_restrict format is a 52-character bitstring where bit N corresponds to zone N+1
+			# Zones are 1-indexed, so zone 29 needs the bit at position 28 (0-indexed from right)
+			# Build string from right to left: 28 zeros, then "1", then 23 zeros
+			zones_restrict = ("0" * 23 + "1" + "0" * 28).reverse.chars.reverse.join
+
+			# Simpler approach: create a 52-char string with bit 28 set to "1"
+			zones_restrict_array = Array.new(52, "0")
+			zones_restrict_array[28] = "1"  # Set bit for zone 29
+			zones_restrict = zones_restrict_array.join
+
+			restricting_hat = create_item("Restricting Hat", zones(:hat), zones_restrict: zones_restrict)
+
+			# Create an item in the ruff zone
+			ruff_item = create_item("Ruff Item", zones(:ruff))
+
+			appearances = Item.appearances_for([restricting_hat, ruff_item], @pet_type)
+			hat_appearance = appearances[restricting_hat.id]
+			ruff_appearance = appearances[ruff_item.id]
+
+			expect(hat_appearance.compatible_with?(ruff_appearance)).to be false
+			expect(ruff_appearance.compatible_with?(hat_appearance)).to be false
+		end
+
+		it "returns true for empty appearances" do
+			# Create items that don't fit the current pet (wrong body_id)
+			hat = create_item("Hat", zones(:hat), body_id: 999)
+			shirt = create_item("Shirt", zones(:shirtdress), body_id: 999)
+
+			appearances = Item.appearances_for([hat, shirt], @pet_type)
+			hat_appearance = appearances[hat.id]
+			shirt_appearance = appearances[shirt.id]
+
+			# Both should be empty (no swf_assets for this pet)
+			expect(hat_appearance).to be_empty
+			expect(shirt_appearance).to be_empty
+
+			# Empty appearances should be compatible
+			expect(hat_appearance.compatible_with?(shirt_appearance)).to be true
+		end
+	end
+
+	describe "#without_item" do
+		it "returns a new outfit without the given item" do
+			hat = create_item("Hat", zones(:hat))
+			outfit_with_hat = @outfit.with_item(hat)
+
+			new_outfit = outfit_with_hat.without_item(hat)
+
+			expect(new_outfit.worn_items).not_to include(hat)
+			expect(outfit_with_hat.worn_items).to include(hat) # Original unchanged
+		end
+
+		it "returns a new outfit instance (immutable)" do
+			hat = create_item("Hat", zones(:hat))
+			outfit_with_hat = @outfit.with_item(hat)
+
+			new_outfit = outfit_with_hat.without_item(hat)
+
+			expect(new_outfit).not_to eq(outfit_with_hat)
+			expect(new_outfit.object_id).not_to eq(outfit_with_hat.object_id)
+		end
+
+		it "does nothing if the item is not worn" do
+			hat = create_item("Hat", zones(:hat))
+
+			new_outfit = @outfit.without_item(hat)
+
+			expect(new_outfit.worn_items).to be_empty
+		end
+	end
+
+	describe "#with_item" do
+		it "adds an item when there are no conflicts" do
+			hat = create_item("Hat", zones(:hat))
+
+			new_outfit = @outfit.with_item(hat)
+
+			expect(new_outfit.worn_items).to include(hat)
+		end
+
+		it "returns a new outfit instance (immutable)" do
+			hat = create_item("Hat", zones(:hat))
+
+			new_outfit = @outfit.with_item(hat)
+
+			expect(new_outfit).not_to eq(@outfit)
+			expect(new_outfit.object_id).not_to eq(@outfit.object_id)
+			expect(@outfit.worn_items).to be_empty # Original unchanged
+		end
+
+		it "is idempotent (adding same item twice has no effect)" do
+			hat = create_item("Hat", zones(:hat))
+
+			outfit1 = @outfit.with_item(hat)
+			outfit2 = outfit1.with_item(hat)
+
+			expect(outfit1.worn_items.size).to eq(1)
+			expect(outfit2.worn_items.size).to eq(1)
+			expect(outfit2.worn_items).to include(hat)
+		end
+
+		it "does not add items that don't fit this pet" do
+			# Create item with wrong body_id
+			hat = create_item("Hat", zones(:hat), body_id: 999)
+
+			new_outfit = @outfit.with_item(hat)
+
+			expect(new_outfit.worn_items).to be_empty
+		end
+
+		context "with conflicting items" do
+			it "moves conflicting item to closet when items occupy the same zone" do
+				hat1 = create_item("Hat 1", zones(:hat))
+				hat2 = create_item("Hat 2", zones(:hat))
+
+				outfit_with_hat1 = @outfit.with_item(hat1)
+				outfit_with_hat2 = outfit_with_hat1.with_item(hat2)
+
+				expect(outfit_with_hat2.worn_items).to include(hat2)
+				expect(outfit_with_hat2.worn_items).not_to include(hat1)
+				expect(outfit_with_hat2.closeted_items).to include(hat1)
+			end
+
+			it "moves conflicting item to closet when new item restricts zone" do
+				# Create item in ruff zone
+				ruff_item = create_item("Ruff Item", zones(:ruff))
+
+				# Create hat that restricts ruff zone (zone 29)
+				# zones_restrict is 0-indexed, so zone 29 needs bit 28 to be "1"
+				zones_restrict_array = Array.new(52, "0")
+				zones_restrict_array[28] = "1"
+				zones_restrict = zones_restrict_array.join
+				restricting_hat = create_item("Restricting Hat", zones(:hat), zones_restrict: zones_restrict)
+
+				# First wear ruff item, then wear restricting hat
+				outfit_with_ruff = @outfit.with_item(ruff_item)
+				outfit_with_hat = outfit_with_ruff.with_item(restricting_hat)
+
+				expect(outfit_with_hat.worn_items).to include(restricting_hat)
+				expect(outfit_with_hat.worn_items).not_to include(ruff_item)
+				expect(outfit_with_hat.closeted_items).to include(ruff_item)
+			end
+
+			it "keeps compatible items when adding new item" do
+				hat = create_item("Hat", zones(:hat))
+				shirt = create_item("Shirt", zones(:shirtdress))
+				pants = create_item("Pants", zones(:trousers))
+
+				outfit1 = @outfit.with_item(hat).with_item(shirt)
+				outfit2 = outfit1.with_item(pants)
+
+				expect(outfit2.worn_items).to include(hat, shirt, pants)
+				expect(outfit2.closeted_items).to be_empty
+			end
+
+			it "can move multiple conflicting items to closet" do
+				hat1 = create_item("Hat 1", zones(:hat))
+				hat2 = create_item("Hat 2", zones(:hat))
+				hat3 = create_item("Hat 3", zones(:hat))
+
+				# Wear hat1 and hat2 by manually building the outfit
+				# (normally you can't, but we're testing the conflict resolution)
+				outfit = @outfit.dup
+				outfit.worn_items << hat1
+				outfit.worn_items << hat2
+
+				# Now add hat3, which should move both hat1 and hat2 to closet
+				outfit_with_hat3 = outfit.with_item(hat3)
+
+				expect(outfit_with_hat3.worn_items).to contain_exactly(hat3)
+				expect(outfit_with_hat3.closeted_items).to contain_exactly(hat1, hat2)
+			end
+
+			it "does not duplicate items in closet if already closeted" do
+				hat1 = create_item("Hat 1", zones(:hat))
+				hat2 = create_item("Hat 2", zones(:hat))
+
+				# Wear hat1
+				outfit1 = @outfit.with_item(hat1)
+
+				# Add hat2 (moves hat1 to closet)
+				outfit2 = outfit1.with_item(hat2)
+
+				# Add hat2 again (should be idempotent, not duplicate hat1 in closet)
+				outfit3 = outfit2.with_item(hat2)
+
+				expect(outfit3.closeted_items.size).to eq(1)
+				expect(outfit3.closeted_items).to include(hat1)
+			end
+		end
+
+		context "edge cases" do
+			it "handles nil item gracefully" do
+				expect { @outfit.with_item(nil) }.not_to raise_error
+			end
+
+			it "works with outfit that has no pet_state" do
+				# This shouldn't happen in practice, but let's be defensive
+				outfit_no_pet = Outfit.new
+				hat = create_item("Hat", zones(:hat))
+
+				# Should not crash, but also won't add the item
+				expect { outfit_no_pet.with_item(hat) }.not_to raise_error
+			end
+		end
+	end
+end