diff --git a/src/main/java/com/example/demo/model/Cart.java b/src/main/java/com/example/demo/model/Cart.java
new file mode 100644
index 0000000..d640ab7
--- /dev/null
+++ b/src/main/java/com/example/demo/model/Cart.java
@@ -0,0 +1,64 @@
+package com.example.demo.model;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+public class Cart {
+
+    private List<LineItem> lineItems;
+    private int totalQuantity;
+
+    public Cart(List<LineItem> lineItems) {
+        this.lineItems = new ArrayList<>(lineItems);
+        calculateTotalQuantity();
+    }
+
+    public List<LineItem> getLineItems() {
+        return Collections.unmodifiableList(lineItems);
+    }
+
+    public int getTotalQuantity() {
+        return totalQuantity;
+    }
+
+    public void addProduct(ProductId productId, ProductOption productOption, int quantity) {
+
+
+        LineItem lineItem = findLineItem(productId, productOption);
+
+        if (lineItem != null) {
+            lineItem.addQuantity(quantity, productOption);
+            calculateTotalQuantity();
+            checkValidQuantity();
+            return;
+        }
+
+        lineItem = new LineItem(productId, productOption, quantity);
+        lineItems.add(lineItem);
+        calculateTotalQuantity();
+        checkValidQuantity();
+    }
+
+    public void checkValidQuantity() {
+        if (totalQuantity > 20) {
+            throw new IllegalArgumentException("담을수 있는 수량을 초과했습니다.");
+        }
+    }
+
+    private void calculateTotalQuantity() {
+        this.totalQuantity = lineItems.stream()
+                .mapToInt(LineItem::getQuantity)
+                .sum();
+    }
+
+
+    private LineItem findLineItem(ProductId productId, ProductOption productOption) {
+        return lineItems.stream()
+                .filter(lineItem ->
+                        lineItem.isSameProduct(productId,productOption))
+                .findFirst()
+                .orElse(null);
+    }
+
+}
diff --git a/src/main/java/com/example/demo/model/LineItem.java b/src/main/java/com/example/demo/model/LineItem.java
new file mode 100644
index 0000000..79204f8
--- /dev/null
+++ b/src/main/java/com/example/demo/model/LineItem.java
@@ -0,0 +1,35 @@
+package com.example.demo.model;
+
+
+public class LineItem {
+
+    private final LineItemId id;
+    private final ProductId productId;
+    private final ProductOption productOption;
+
+    private int quantity;
+
+
+    public LineItem(ProductId productId, ProductOption productOption, int quantity) {
+        this.id = LineItemId.generate();
+        this.productId = productId;
+        this.productOption = productOption;
+        this.quantity = quantity;
+    }
+
+    public int getQuantity() {
+        return quantity;
+    }
+
+
+    public void addQuantity(int quantity, ProductOption productOption) {
+        if(!this.productOption.equals(productOption)) {
+            return;
+        }
+        this.quantity += quantity;
+    }
+
+    public boolean isSameProduct(ProductId productId, ProductOption productOption) {
+        return this.productId.equals(productId) && this.productOption.equals(productOption);
+    }
+}
diff --git a/src/main/java/com/example/demo/model/LineItemId.java b/src/main/java/com/example/demo/model/LineItemId.java
new file mode 100644
index 0000000..c0e1f57
--- /dev/null
+++ b/src/main/java/com/example/demo/model/LineItemId.java
@@ -0,0 +1,12 @@
+package com.example.demo.model;
+
+import java.util.UUID;
+
+public record LineItemId(
+     String id
+) {
+
+    public static LineItemId generate() {
+        return new LineItemId("lineItemId-" + UUID.randomUUID());
+    }
+}
diff --git a/src/main/java/com/example/demo/model/Product.java b/src/main/java/com/example/demo/model/Product.java
new file mode 100644
index 0000000..f0b49f1
--- /dev/null
+++ b/src/main/java/com/example/demo/model/Product.java
@@ -0,0 +1,34 @@
+package com.example.demo.model;
+
+public class Product {
+
+    private ProductId id;
+    private String name;
+    private int price;
+
+    public Product(ProductId id, String name, int price) {
+        this.id = id;
+        this.name = name;
+        this.price = price;
+    }
+
+    public ProductId getId() {
+        return id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public int getPrice() {
+        return price;
+    }
+
+    public void changePrice(int price) {
+        this.price = price;
+    }
+
+    public void changeName(String name) {
+        this.name = name;
+    }
+}
diff --git a/src/main/java/com/example/demo/model/ProductId.java b/src/main/java/com/example/demo/model/ProductId.java
new file mode 100644
index 0000000..4951e6b
--- /dev/null
+++ b/src/main/java/com/example/demo/model/ProductId.java
@@ -0,0 +1,6 @@
+package com.example.demo.model;
+
+public record ProductId (
+        String id
+){
+}
diff --git a/src/main/java/com/example/demo/model/ProductOption.java b/src/main/java/com/example/demo/model/ProductOption.java
new file mode 100644
index 0000000..aa16fdb
--- /dev/null
+++ b/src/main/java/com/example/demo/model/ProductOption.java
@@ -0,0 +1,7 @@
+package com.example.demo.model;
+
+public record ProductOption(
+        String color,
+        String size
+) {
+}
diff --git a/src/test/java/com/example/demo/model/CartTest.java b/src/test/java/com/example/demo/model/CartTest.java
new file mode 100644
index 0000000..972473e
--- /dev/null
+++ b/src/test/java/com/example/demo/model/CartTest.java
@@ -0,0 +1,101 @@
+package com.example.demo.model;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import java.util.List;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+class CartTest {
+
+    private Product product1;
+    private Product product2;
+    private ProductOption productOption1;
+    private ProductOption productOption2;
+
+    @BeforeEach
+    void setUp() {
+        product1 = new Product(new ProductId("product-1"), "product #1", 5000);
+        product2 = new Product(new ProductId("product-2"), "product #2", 3000);
+
+        productOption1 = new ProductOption("red", "M");
+        productOption2 = new ProductOption("black", "L");
+    }
+
+    @Test
+    @DisplayName("빈 장바구니의 수량은 0이다.")
+    void cartTotalQuantityIsZero() {
+        Cart cart = new Cart(List.of());
+
+        assertThat(cart.getTotalQuantity()).isEqualTo(0);
+    }
+
+    @Test
+    @DisplayName("빈 장바구니에 물건 추가하면 장바구니의 전체수량은 추가한 수량과 같다.")
+    void addProduct() {
+        Cart cart = new Cart(List.of());
+
+        int quantity = 1;
+        cart.addProduct(product1.getId(), productOption1, quantity);
+
+        assertThat(cart.getTotalQuantity()).isEqualTo(quantity);
+    }
+
+    @Test
+    @DisplayName("장바구니에 이미 있는 물건 추가하면 전체 수량은 이미 있던 수량과 새로 추가하는 수량의 합이다.")
+    void addExistingProduct() {
+
+        int oldQuantity = 1;
+        Cart cart = new Cart(List.of(
+                createLineItem(product1, productOption1, oldQuantity)
+        ));
+
+        int newQuantity = 1;
+        cart.addProduct(product1.getId(), productOption1, newQuantity);
+
+        assertThat(cart.getLineItems()).hasSize(1);
+        assertThat(cart.getTotalQuantity()).isEqualTo(oldQuantity + newQuantity);
+    }
+
+    @Test
+    @DisplayName("장바구니에 새로운 있는 물건 추가하면 전체 수량은 이미 있던 물건의 수량과 " +
+            "새로 추가하는 물건의 수량의 합이다.")
+    void addNewProduct() {
+
+        int oldQuantity = 1;
+        Cart cart = new Cart(List.of(
+                createLineItem(product2, productOption2, oldQuantity)
+        ));
+
+        int newQuantity = 1;
+        cart.addProduct(product1.getId(), productOption1, newQuantity);
+
+        assertThat(cart.getLineItems()).hasSize(2);
+        assertThat(cart.getTotalQuantity()).isEqualTo(oldQuantity + newQuantity);
+    }
+
+    @Test
+    @DisplayName("전체 장바구니의 수량이 20개가 넘어가면 예외가 발생한다.")
+    void totalQuantityCanNotOverLimit() {
+        Cart cart = new Cart(List.of(
+                createLineItem(product1, productOption1, 19)
+        ));
+
+        int newQuantity = 5;
+
+        assertThatThrownBy(
+                () -> cart.addProduct(product1.getId(), productOption1, newQuantity)
+        ).isInstanceOf(IllegalArgumentException.class);
+
+    }
+
+
+
+    private LineItem createLineItem(Product product, ProductOption productOption, int quantity) {
+        return new LineItem(product.getId(), productOption, quantity);
+    }
+
+}
diff --git a/src/test/java/com/example/demo/model/LineItemIdTest.java b/src/test/java/com/example/demo/model/LineItemIdTest.java
new file mode 100644
index 0000000..0883233
--- /dev/null
+++ b/src/test/java/com/example/demo/model/LineItemIdTest.java
@@ -0,0 +1,30 @@
+package com.example.demo.model;
+
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.jupiter.api.Assertions.*;
+
+class LineItemIdTest {
+
+    @Test
+    @DisplayName("같은 값이면 같은 객체로 취급된다.")
+    void sameLineItemId() {
+        LineItemId id1 = new LineItemId("LineItem-1");
+        LineItemId id2 = new LineItemId("LineItem-1");
+
+        assertThat(id1).isEqualTo(id2);
+    }
+
+    @Test
+    @DisplayName("generate()를 사용하면 서로다른 아이디가 생성된다.")
+    void lineItemIdIsUnique() {
+        LineItemId id1 = LineItemId.generate();
+        LineItemId id2 = LineItemId.generate();
+
+        assertThat(id1).isNotEqualTo(id2);
+    }
+
+
+}
diff --git a/src/test/java/com/example/demo/model/LineItemTest.java b/src/test/java/com/example/demo/model/LineItemTest.java
new file mode 100644
index 0000000..659e53f
--- /dev/null
+++ b/src/test/java/com/example/demo/model/LineItemTest.java
@@ -0,0 +1,42 @@
+package com.example.demo.model;
+
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+
+class LineItemTest {
+
+    @Test
+    @DisplayName("같은 상품과 옵션일 경우, 수량을 추가할 수 있어야 한다.")
+    void isSameProduct(){
+        ProductId productId = new ProductId("productId");
+        ProductOption productOption = new ProductOption("red", "M");
+        int quantity = 1;
+        int delta = 5;
+
+        LineItem lineItem = new LineItem(productId, productOption, quantity);
+        lineItem.addQuantity(delta, productOption);
+
+        assertThat(lineItem.isSameProduct(productId, new ProductOption("red", "M"))).isTrue();
+        assertThat(lineItem.getQuantity()).isEqualTo(quantity + delta);
+
+    }
+
+    @Test
+    @DisplayName("같은 상품이라도 옵션이 다르면, 수량은 추가되지 않는다.")
+    void sameProductAndDifferentOption(){
+        ProductId productId = new ProductId("productId");
+        ProductOption productOption = new ProductOption("red", "M");
+        int quantity = 1;
+        int delta = 5;
+        LineItem lineItem = new LineItem(productId, productOption, quantity);
+
+        ProductOption productOption2 = new ProductOption("black", "M");
+        lineItem.addQuantity(delta, productOption2);
+
+        assertThat(lineItem.isSameProduct(productId, productOption2)).isFalse();
+        assertThat(lineItem.getQuantity()).isEqualTo(quantity);
+    }
+}
diff --git a/src/test/java/com/example/demo/model/ProductIdTest.java b/src/test/java/com/example/demo/model/ProductIdTest.java
new file mode 100644
index 0000000..e8361fa
--- /dev/null
+++ b/src/test/java/com/example/demo/model/ProductIdTest.java
@@ -0,0 +1,20 @@
+package com.example.demo.model;
+
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.jupiter.api.Assertions.*;
+
+class ProductIdTest {
+
+    @Test
+    @DisplayName("같은 값이면 같은 객체로 취급된다.")
+    void sameProductId() {
+        ProductId id1 = new ProductId("productId-1");
+        ProductId id2 = new ProductId("productId-1");
+
+        assertThat(id1).isEqualTo(id2);
+    }
+
+}
diff --git a/src/test/java/com/example/demo/model/ProductOptionTest.java b/src/test/java/com/example/demo/model/ProductOptionTest.java
new file mode 100644
index 0000000..9f148df
--- /dev/null
+++ b/src/test/java/com/example/demo/model/ProductOptionTest.java
@@ -0,0 +1,28 @@
+package com.example.demo.model;
+
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class ProductOptionTest {
+
+    @Test
+    @DisplayName("값이 같으면 같은 객체로 취급된다.")
+    void sameValue() {
+        ProductOption option1 = new ProductOption("red", "M");
+        ProductOption option2 = new ProductOption("red", "M");
+
+        assertThat(option1).isEqualTo(option2);
+    }
+
+    @Test
+    @DisplayName("값이 다르면 다른 객체로 취급된다.")
+    void differentValue() {
+        ProductOption option1 = new ProductOption("red", "M");
+        ProductOption option2 = new ProductOption("black", "M");
+
+        assertThat(option1).isNotEqualTo(option2);
+    }
+
+}
diff --git a/src/test/java/com/example/demo/model/ProductTest.java b/src/test/java/com/example/demo/model/ProductTest.java
new file mode 100644
index 0000000..6838595
--- /dev/null
+++ b/src/test/java/com/example/demo/model/ProductTest.java
@@ -0,0 +1,34 @@
+package com.example.demo.model;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class ProductTest {
+
+    private Product product;
+
+    @BeforeEach
+    void setUp() {
+        product = new Product(new ProductId("product-1"), "Product #1", 5000);
+    }
+
+    @Test
+    void changeProductName(){
+
+        String newName = "NewProduct";
+        product.changeName(newName);
+
+        assertThat(product.getName()).isEqualTo(newName);
+    }
+
+    @Test
+    void changeProductPrice(){
+        int newPrice = 10000;
+        product.changePrice(newPrice);
+
+        assertThat(product.getPrice()).isEqualTo(newPrice);
+    }
+
+}