diff --git a/README.md b/README.md
index 498506166..932e5e215 100644
--- a/README.md
+++ b/README.md
@@ -6,4 +6,25 @@
 * 모든 피드백을 완료하면 다음 단계를 도전하고 앞의 과정을 반복한다.
 
 ## 온라인 코드 리뷰 과정
-* [텍스트와 이미지로 살펴보는 온라인 코드 리뷰 과정](https://github.com/next-step/nextstep-docs/tree/master/codereview)
\ No newline at end of file
+* [텍스트와 이미지로 살펴보는 온라인 코드 리뷰 과정](https://github.com/next-step/nextstep-docs/tree/master/codereview)
+
+## 수강 신청 기능 요구사항
+- 과정(Course)은 기수 단위로 운영하며, 여러 개의 강의(Session)를 가질 수 있다.
+- 강의는 시작일과 종료일을 가진다.
+- 강의는 강의 커버 이미지 정보를 가진다.
+- 이미지 크기는 1MB 이하여야 한다.
+- 이미지 타입은 gif, jpg(jpeg 포함), png, svg만 허용한다.
+- 이미지의 width는 300픽셀, height는 200픽셀 이상이어야 하며, width와 height의 비율은 3:2여야 한다.
+- 강의는 무료 강의와 유료 강의로 나뉜다.
+- 무료 강의는 최대 수강 인원 제한이 없다.
+- 유료 강의는 강의 최대 수강 인원을 초과할 수 없다.
+- 유료 강의는 수강생이 결제한 금액과 수강료가 일치할 때 수강 신청이 가능하다.
+- 강의 상태는 준비중, 모집중, 종료 3가지 상태를 가진다.
+- 강의 수강신청은 강의 상태가 모집중일 때만 가능하다.
+- 유료 강의의 경우 결제는 이미 완료한 것으로 가정하고 이후 과정을 구현한다.
+- 결제를 완료한 결제 정보는 payments 모듈을 통해 관리되며, 결제 정보는 Payment 객체에 담겨 반한된다.
+
+## 프로그래밍 요구사항
+- DB 테이블 설계 없이 도메인 모델부터 구현한다.
+- 도메인 모델은 TDD로 구현한다.
+- 단, Service 클래스는 단위 테스트가 없어도 된다.
diff --git a/src/main/java/nextstep/courses/InvalidImageFileException.java b/src/main/java/nextstep/courses/InvalidImageFileException.java
new file mode 100644
index 000000000..152ded6b0
--- /dev/null
+++ b/src/main/java/nextstep/courses/InvalidImageFileException.java
@@ -0,0 +1,7 @@
+package nextstep.courses;
+
+public class InvalidImageFileException extends RuntimeException {
+    public InvalidImageFileException(String message) {
+        super(message);
+    }
+}
diff --git a/src/main/java/nextstep/courses/SessionUnregistrableException.java b/src/main/java/nextstep/courses/SessionUnregistrableException.java
new file mode 100644
index 000000000..a9c00059d
--- /dev/null
+++ b/src/main/java/nextstep/courses/SessionUnregistrableException.java
@@ -0,0 +1,10 @@
+package nextstep.courses;
+
+public class SessionUnregistrableException extends RuntimeException{
+    public SessionUnregistrableException(){
+    }
+
+    public SessionUnregistrableException(String message) {
+        super(message);
+    }
+}
diff --git a/src/main/java/nextstep/courses/domain/BaseEntity.java b/src/main/java/nextstep/courses/domain/BaseEntity.java
new file mode 100644
index 000000000..7d9172da9
--- /dev/null
+++ b/src/main/java/nextstep/courses/domain/BaseEntity.java
@@ -0,0 +1,21 @@
+package nextstep.courses.domain;
+
+import nextstep.courses.domain.session.Period;
+
+import java.time.LocalDate;
+
+public class BaseEntity {
+    private final Long id;
+    private final String title;
+    private final Period period;
+
+    public BaseEntity(Long id, String title, LocalDate startDate, LocalDate endDate) {
+        this(id, title, new Period(startDate, endDate));
+    }
+
+    public BaseEntity(Long id, String title, Period period) {
+        this.id = id;
+        this.title = title;
+        this.period = period;
+    }
+}
diff --git a/src/main/java/nextstep/courses/domain/Course.java b/src/main/java/nextstep/courses/domain/course/Course.java
similarity index 96%
rename from src/main/java/nextstep/courses/domain/Course.java
rename to src/main/java/nextstep/courses/domain/course/Course.java
index 0f6971604..1c935f2fc 100644
--- a/src/main/java/nextstep/courses/domain/Course.java
+++ b/src/main/java/nextstep/courses/domain/course/Course.java
@@ -1,4 +1,4 @@
-package nextstep.courses.domain;
+package nextstep.courses.domain.course;
 
 import java.time.LocalDateTime;
 
diff --git a/src/main/java/nextstep/courses/domain/CourseRepository.java b/src/main/java/nextstep/courses/domain/course/CourseRepository.java
similarity index 71%
rename from src/main/java/nextstep/courses/domain/CourseRepository.java
rename to src/main/java/nextstep/courses/domain/course/CourseRepository.java
index 6aaeb638d..28180d25e 100644
--- a/src/main/java/nextstep/courses/domain/CourseRepository.java
+++ b/src/main/java/nextstep/courses/domain/course/CourseRepository.java
@@ -1,4 +1,4 @@
-package nextstep.courses.domain;
+package nextstep.courses.domain.course;
 
 public interface CourseRepository {
     int save(Course course);
diff --git a/src/main/java/nextstep/courses/domain/image/Image.java b/src/main/java/nextstep/courses/domain/image/Image.java
new file mode 100644
index 000000000..126591c60
--- /dev/null
+++ b/src/main/java/nextstep/courses/domain/image/Image.java
@@ -0,0 +1,13 @@
+package nextstep.courses.domain.image;
+
+public class Image {
+    private final ImageSize size;
+    private final ImageDimension imageDimension;
+    private final ImageFileExtension fileExtension;
+
+    public Image(int size, int width, int height, String fileExtension) {
+        this.size = new ImageSize(size);
+        this.imageDimension = new ImageDimension(width, height);
+        this.fileExtension = ImageFileExtension.from(fileExtension);
+    }
+}
diff --git a/src/main/java/nextstep/courses/domain/image/ImageDimension.java b/src/main/java/nextstep/courses/domain/image/ImageDimension.java
new file mode 100644
index 000000000..64fbeaf93
--- /dev/null
+++ b/src/main/java/nextstep/courses/domain/image/ImageDimension.java
@@ -0,0 +1,28 @@
+package nextstep.courses.domain.image;
+
+import nextstep.courses.InvalidImageFileException;
+
+public class ImageDimension {
+    private final static int MIN_WIDTH = 300; // 300 px
+    private final static int MIN_HEIGHT = 200; // 200 px
+    private final static double ASPECT_RATIO = 1.5; // width : height = 3 : 2
+
+    private final int width;
+    private final int height;
+
+    public ImageDimension(int width, int height) {
+        if (!isValidWidthAndHeight(width, height)) {
+            throw new InvalidImageFileException(String.format("이미지는 가로 %spx 이상, 세로 %spx 이상, 가로 세로 비율이 %s:1 이어야 합니다.", MIN_WIDTH, MIN_HEIGHT, ASPECT_RATIO));
+        }
+        this.width = width;
+        this.height = height;
+    }
+
+    private boolean isValidWidthAndHeight(int width, int height) {
+        return width >= MIN_WIDTH && height >= MIN_HEIGHT && isValidRatio(width, height);
+    }
+
+    private boolean isValidRatio(int width, int height) {
+        return (double) width / height == ASPECT_RATIO;
+    }
+}
diff --git a/src/main/java/nextstep/courses/domain/image/ImageFileExtension.java b/src/main/java/nextstep/courses/domain/image/ImageFileExtension.java
new file mode 100644
index 000000000..99b1edc20
--- /dev/null
+++ b/src/main/java/nextstep/courses/domain/image/ImageFileExtension.java
@@ -0,0 +1,37 @@
+package nextstep.courses.domain.image;
+
+import nextstep.courses.InvalidImageFileException;
+
+import java.util.Arrays;
+import java.util.stream.Collectors;
+
+public enum ImageFileExtension {
+    GIF("gif"),
+    JPG("jpg"),
+    JPEG("jpeg"),
+    PNG("png"),
+    SVG("svg");
+
+    private final String value;
+
+    ImageFileExtension(String value) {
+        this.value = value;
+    }
+
+    private String value() {
+        return value;
+    }
+
+    static ImageFileExtension from(String value) {
+        return Arrays.stream(ImageFileExtension.values())
+                .filter(fileExtension -> fileExtension.value.equals(value))
+                .findFirst()
+                .orElseThrow(() -> new InvalidImageFileException(String.format("이미지 파일은 %s 중에 하나의 형태여야 합니다.", possibleFileExtensions())));
+    }
+
+    private static String possibleFileExtensions() {
+        return Arrays.stream(ImageFileExtension.values())
+                .map(ImageFileExtension::value)
+                .collect(Collectors.joining(", "));
+    }
+}
diff --git a/src/main/java/nextstep/courses/domain/image/ImageSize.java b/src/main/java/nextstep/courses/domain/image/ImageSize.java
new file mode 100644
index 000000000..7688e5e54
--- /dev/null
+++ b/src/main/java/nextstep/courses/domain/image/ImageSize.java
@@ -0,0 +1,19 @@
+package nextstep.courses.domain.image;
+
+import nextstep.courses.InvalidImageFileException;
+
+class ImageSize {
+    private final static int MAX_SIZE = 1_024; // 1024 Byte
+    private final int size;
+
+    ImageSize(int size) {
+        if (!isValidSize(size)) {
+            throw new InvalidImageFileException(String.format("이미지 사이즈는 %sB 이하여야 합니다.", MAX_SIZE));
+        }
+        this.size = size;
+    }
+
+    private boolean isValidSize(int size) {
+        return size <= MAX_SIZE;
+    }
+}
diff --git a/src/main/java/nextstep/courses/domain/session/Capacity.java b/src/main/java/nextstep/courses/domain/session/Capacity.java
new file mode 100644
index 000000000..83d571125
--- /dev/null
+++ b/src/main/java/nextstep/courses/domain/session/Capacity.java
@@ -0,0 +1,22 @@
+package nextstep.courses.domain.session;
+
+public class Capacity {
+    private final static int UNLIMITED = -1;
+    private final int capacity;
+
+    public Capacity() {
+        this(UNLIMITED);
+    }
+
+    public Capacity(int capacity) {
+        this.capacity = capacity;
+    }
+
+    public boolean isUnlimited() {
+        return capacity == UNLIMITED;
+    }
+
+    public boolean isGreaterThan(int value) {
+        return capacity > value;
+    }
+}
diff --git a/src/main/java/nextstep/courses/domain/session/EnrollmentCondition.java b/src/main/java/nextstep/courses/domain/session/EnrollmentCondition.java
new file mode 100644
index 000000000..ddf60a27b
--- /dev/null
+++ b/src/main/java/nextstep/courses/domain/session/EnrollmentCondition.java
@@ -0,0 +1,32 @@
+package nextstep.courses.domain.session;
+
+import nextstep.payments.domain.Payment;
+import nextstep.users.domain.NsUser;
+
+/**
+ * 개인별 수강 신청 가능 조건 값을 관리하는 도메인
+ */
+public class EnrollmentCondition {
+    private final NsUser user;
+    private final Payment payment;
+
+    public EnrollmentCondition(NsUser user, Payment payment) {
+        if (!paidBySameUser(user, payment)) {
+            throw new IllegalArgumentException("수강 신청자와 결제자 정보가 불일치합니다.");
+        }
+        this.user = user;
+        this.payment = payment;
+    }
+
+    private boolean paidBySameUser(NsUser user, Payment payment) {
+        return payment.isPaidBy(user.getId());
+    }
+
+    public NsUser getUser() {
+        return user;
+    }
+
+    public boolean hasPaid(Long sessionId, long price) {
+        return payment.isPaidFor(sessionId) && payment.isSameAmount(price);
+    }
+}
diff --git a/src/main/java/nextstep/courses/domain/session/Period.java b/src/main/java/nextstep/courses/domain/session/Period.java
new file mode 100644
index 000000000..909bffe84
--- /dev/null
+++ b/src/main/java/nextstep/courses/domain/session/Period.java
@@ -0,0 +1,13 @@
+package nextstep.courses.domain.session;
+
+import java.time.LocalDate;
+
+public class Period {
+    private final LocalDate startDate;
+    private final LocalDate endDate;
+
+    public Period(LocalDate startDate, LocalDate endDate) {
+        this.startDate = startDate;
+        this.endDate = endDate;
+    }
+}
diff --git a/src/main/java/nextstep/courses/domain/session/Session.java b/src/main/java/nextstep/courses/domain/session/Session.java
new file mode 100644
index 000000000..2ad502ad0
--- /dev/null
+++ b/src/main/java/nextstep/courses/domain/session/Session.java
@@ -0,0 +1,52 @@
+package nextstep.courses.domain.session;
+
+import nextstep.courses.SessionUnregistrableException;
+import nextstep.courses.domain.*;
+import nextstep.courses.domain.image.Image;
+import nextstep.courses.domain.session.type.Free;
+import nextstep.courses.domain.session.type.Paid;
+import nextstep.courses.domain.session.type.SessionType;
+
+import java.time.LocalDate;
+
+public class Session {
+    private final BaseEntity baseEntity;
+    private final Image image;
+    private SessionStatus status;
+    private final SessionType type;
+
+    public Session(Long id, String title, Image image, SessionStatus status, SessionType type, LocalDate startDate, LocalDate endDate) {
+        this.baseEntity = new BaseEntity(id, title, new Period(startDate, endDate));
+        this.image = image;
+        this.status = status;
+        this.type = type;
+    }
+
+    public void openRecruiting() {
+        this.status = SessionStatus.RECRUITING;
+    }
+
+    public boolean isRecruiting() {
+        return this.status == SessionStatus.RECRUITING;
+    }
+
+    public boolean canEnroll(EnrollmentCondition request) {
+        return this.type.canEnroll(request);
+    }
+
+    public String currentStatusToHumanReadable() {
+        return this.status.name();
+    }
+
+    public String typeToHumanReadable() {
+        return this.type.toHumanReadableTypeName();
+    }
+
+    public static Session createFreeSession(String title, Image image) {
+        return new Session(null, title, image, SessionStatus.PREPARING, new Free(), LocalDate.now(), LocalDate.MAX);
+    }
+
+    public static Session createPaidSession(long id, String title, Image image, long price) {
+        return new Session(null, title, image, SessionStatus.PREPARING, new Paid(id, price), LocalDate.now(), LocalDate.MAX);
+    }
+}
diff --git a/src/main/java/nextstep/courses/domain/session/SessionEnrollment.java b/src/main/java/nextstep/courses/domain/session/SessionEnrollment.java
new file mode 100644
index 000000000..93bc23997
--- /dev/null
+++ b/src/main/java/nextstep/courses/domain/session/SessionEnrollment.java
@@ -0,0 +1,53 @@
+package nextstep.courses.domain.session;
+
+import nextstep.courses.SessionUnregistrableException;
+import nextstep.users.domain.NsUsers;
+
+/**
+ * 강의 정원 및 현재 등록 인원을 관리하는 도메인
+ */
+public class SessionEnrollment {
+    private final Capacity maxCapacity;
+    private final NsUsers enrolledUsers;
+    private final Session session;
+
+    public SessionEnrollment(Session session) {
+        this(new Capacity(), new NsUsers(), session);
+    }
+
+    public SessionEnrollment(int maxCapacity, Session session) {
+        this(new Capacity(maxCapacity), new NsUsers(), session);
+    }
+
+    public SessionEnrollment(Capacity maxCapacity, NsUsers enrolledUsers, Session session) {
+        this.maxCapacity = maxCapacity;
+        this.enrolledUsers = enrolledUsers;
+        this.session = session;
+    }
+
+    public void enroll(EnrollmentCondition condition) {
+        checkEnrollable(condition);
+        this.enrolledUsers.addUser(condition.getUser());
+    }
+
+    private void checkEnrollable(EnrollmentCondition condition) {
+        if (!session.isRecruiting()) {
+            throw new SessionUnregistrableException(String.format("%s 상태인 강의는 수강신청할 수 없습니다.", session.currentStatusToHumanReadable()));
+        }
+
+        if (!session.canEnroll(condition)) {
+            throw new SessionUnregistrableException(String.format("%s 강의 수강 신청 조건 미달로 신청할 수 없습니다.", session.typeToHumanReadable()));
+        }
+
+        if (!hasCapacity()) {
+            throw new SessionUnregistrableException("정원 초과로 수강신청할 수 없습니다.");
+        }
+    }
+
+    private boolean hasCapacity() {
+        if (maxCapacity.isUnlimited()) {
+            return true;
+        }
+        return enrolledUsers.isLessThan(maxCapacity);
+    }
+}
diff --git a/src/main/java/nextstep/courses/domain/session/SessionStatus.java b/src/main/java/nextstep/courses/domain/session/SessionStatus.java
new file mode 100644
index 000000000..d565d88b1
--- /dev/null
+++ b/src/main/java/nextstep/courses/domain/session/SessionStatus.java
@@ -0,0 +1,5 @@
+package nextstep.courses.domain.session;
+
+public enum SessionStatus {
+    PREPARING, RECRUITING, COMPLETED
+}
diff --git a/src/main/java/nextstep/courses/domain/session/type/Free.java b/src/main/java/nextstep/courses/domain/session/type/Free.java
new file mode 100644
index 000000000..4051edc9c
--- /dev/null
+++ b/src/main/java/nextstep/courses/domain/session/type/Free.java
@@ -0,0 +1,18 @@
+package nextstep.courses.domain.session.type;
+
+import nextstep.courses.domain.session.EnrollmentCondition;
+
+public class Free implements SessionType {
+    public Free() {
+    }
+
+    @Override
+    public boolean canEnroll(EnrollmentCondition request) {
+        return true;
+    }
+
+    @Override
+    public String toHumanReadableTypeName() {
+        return "무료";
+    }
+}
diff --git a/src/main/java/nextstep/courses/domain/session/type/Paid.java b/src/main/java/nextstep/courses/domain/session/type/Paid.java
new file mode 100644
index 000000000..5147cbfa3
--- /dev/null
+++ b/src/main/java/nextstep/courses/domain/session/type/Paid.java
@@ -0,0 +1,23 @@
+package nextstep.courses.domain.session.type;
+
+import nextstep.courses.domain.session.EnrollmentCondition;
+
+public class Paid implements SessionType {
+    private final long sessionId;
+    private final long price;
+
+    public Paid(long sessionId, long price) {
+        this.sessionId = sessionId;
+        this.price = price;
+    }
+
+    @Override
+    public boolean canEnroll(EnrollmentCondition condition) {
+        return condition.hasPaid(this.sessionId, price);
+    }
+
+    @Override
+    public String toHumanReadableTypeName() {
+        return "유료";
+    }
+}
diff --git a/src/main/java/nextstep/courses/domain/session/type/SessionType.java b/src/main/java/nextstep/courses/domain/session/type/SessionType.java
new file mode 100644
index 000000000..1dd7bd61c
--- /dev/null
+++ b/src/main/java/nextstep/courses/domain/session/type/SessionType.java
@@ -0,0 +1,9 @@
+package nextstep.courses.domain.session.type;
+
+import nextstep.courses.domain.session.EnrollmentCondition;
+
+public interface SessionType {
+    boolean canEnroll(EnrollmentCondition request);
+
+    String toHumanReadableTypeName();
+}
diff --git a/src/main/java/nextstep/courses/infrastructure/JdbcCourseRepository.java b/src/main/java/nextstep/courses/infrastructure/JdbcCourseRepository.java
index f9122cbe3..7489afc31 100644
--- a/src/main/java/nextstep/courses/infrastructure/JdbcCourseRepository.java
+++ b/src/main/java/nextstep/courses/infrastructure/JdbcCourseRepository.java
@@ -1,7 +1,7 @@
 package nextstep.courses.infrastructure;
 
-import nextstep.courses.domain.Course;
-import nextstep.courses.domain.CourseRepository;
+import nextstep.courses.domain.course.Course;
+import nextstep.courses.domain.course.CourseRepository;
 import org.springframework.jdbc.core.JdbcOperations;
 import org.springframework.jdbc.core.RowMapper;
 import org.springframework.stereotype.Repository;
diff --git a/src/main/java/nextstep/payments/domain/Payment.java b/src/main/java/nextstep/payments/domain/Payment.java
index 57d833f85..b7b482109 100644
--- a/src/main/java/nextstep/payments/domain/Payment.java
+++ b/src/main/java/nextstep/payments/domain/Payment.java
@@ -19,6 +19,10 @@ public class Payment {
     public Payment() {
     }
 
+    public Payment(Long sessionId, Long nsUserId, Long amount) {
+        this(null, sessionId, nsUserId, amount);
+    }
+
     public Payment(String id, Long sessionId, Long nsUserId, Long amount) {
         this.id = id;
         this.sessionId = sessionId;
@@ -26,4 +30,16 @@ public Payment(String id, Long sessionId, Long nsUserId, Long amount) {
         this.amount = amount;
         this.createdAt = LocalDateTime.now();
     }
+
+    public boolean isSameAmount(long amount) {
+        return this.amount == amount;
+    }
+
+    public boolean isPaidFor(Long sessionId) {
+        return sessionId.equals(this.sessionId);
+    }
+
+    public boolean isPaidBy(Long userId) {
+        return userId.equals(this.nsUserId);
+    }
 }
diff --git a/src/main/java/nextstep/users/domain/NsUser.java b/src/main/java/nextstep/users/domain/NsUser.java
index 62ec5138c..13aa0591c 100755
--- a/src/main/java/nextstep/users/domain/NsUser.java
+++ b/src/main/java/nextstep/users/domain/NsUser.java
@@ -1,7 +1,5 @@
 package nextstep.users.domain;
 
-import nextstep.qna.UnAuthorizedException;
-
 import java.time.LocalDateTime;
 import java.util.Objects;
 
@@ -43,78 +41,20 @@ public Long getId() {
         return id;
     }
 
-    public String getUserId() {
-        return userId;
-    }
-
-    public NsUser setUserId(String userId) {
-        this.userId = userId;
-        return this;
-    }
-
-    public String getPassword() {
-        return password;
-    }
-
-    public NsUser setPassword(String password) {
-        this.password = password;
-        return this;
-    }
-
-    public String getName() {
-        return name;
-    }
-
-    public NsUser setName(String name) {
-        this.name = name;
-        return this;
-    }
-
-    public String getEmail() {
-        return email;
-    }
-
-    public NsUser setEmail(String email) {
-        this.email = email;
-        return this;
-    }
-
-    public void update(NsUser loginUser, NsUser target) {
-        if (!matchUserId(loginUser.getUserId())) {
-            throw new UnAuthorizedException();
-        }
-
-        if (!matchPassword(target.getPassword())) {
-            throw new UnAuthorizedException();
-        }
-
-        this.name = target.name;
-        this.email = target.email;
-    }
-
-    public boolean matchUser(NsUser target) {
-        return matchUserId(target.getUserId());
-    }
-
-    private boolean matchUserId(String userId) {
-        return this.userId.equals(userId);
-    }
-
-    public boolean matchPassword(String targetPassword) {
-        return password.equals(targetPassword);
+    public boolean isGuestUser() {
+        return false;
     }
 
-    public boolean equalsNameAndEmail(NsUser target) {
-        if (Objects.isNull(target)) {
-            return false;
-        }
-
-        return name.equals(target.name) &&
-                email.equals(target.email);
+    @Override
+    public boolean equals(Object o) {
+        if (o == null || getClass() != o.getClass()) return false;
+        NsUser nsUser = (NsUser) o;
+        return Objects.equals(id, nsUser.id) && Objects.equals(userId, nsUser.userId) && Objects.equals(name, nsUser.name) && Objects.equals(email, nsUser.email);
     }
 
-    public boolean isGuestUser() {
-        return false;
+    @Override
+    public int hashCode() {
+        return Objects.hash(id, userId, name, email);
     }
 
     private static class GuestNsUser extends NsUser {
diff --git a/src/main/java/nextstep/users/domain/NsUsers.java b/src/main/java/nextstep/users/domain/NsUsers.java
new file mode 100644
index 000000000..ae10684d8
--- /dev/null
+++ b/src/main/java/nextstep/users/domain/NsUsers.java
@@ -0,0 +1,26 @@
+package nextstep.users.domain;
+
+import nextstep.courses.domain.session.Capacity;
+
+import java.util.HashSet;
+import java.util.Set;
+
+public class NsUsers {
+    private final Set<NsUser> users;
+
+    public NsUsers() {
+        this(new HashSet<>());
+    }
+
+    public NsUsers(Set<NsUser> users) {
+        this.users = users;
+    }
+
+    public void addUser(NsUser user) {
+        this.users.add(user);
+    }
+
+    public boolean isLessThan(Capacity capacity) {
+        return capacity.isGreaterThan(this.users.size());
+    }
+}
diff --git a/src/test/java/nextstep/courses/domain/image/ImageDimensionTest.java b/src/test/java/nextstep/courses/domain/image/ImageDimensionTest.java
new file mode 100644
index 000000000..50c07ebd2
--- /dev/null
+++ b/src/test/java/nextstep/courses/domain/image/ImageDimensionTest.java
@@ -0,0 +1,19 @@
+package nextstep.courses.domain.image;
+
+import nextstep.courses.InvalidImageFileException;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
+
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+class ImageDimensionTest {
+    @ParameterizedTest
+    @CsvSource(value = {"90,60", "300,300"})
+    void 이미지_너비와_높이와_비율에_제한이_있다(int width, int height) {
+        assertThatThrownBy(() -> new ImageDimension(90, 60))
+                .isInstanceOf(InvalidImageFileException.class);
+
+        assertThatThrownBy(() -> new ImageDimension(300, 300))
+                .isInstanceOf(InvalidImageFileException.class);
+    }
+}
\ No newline at end of file
diff --git a/src/test/java/nextstep/courses/domain/image/ImageFileExtensionTest.java b/src/test/java/nextstep/courses/domain/image/ImageFileExtensionTest.java
new file mode 100644
index 000000000..6390c7c8b
--- /dev/null
+++ b/src/test/java/nextstep/courses/domain/image/ImageFileExtensionTest.java
@@ -0,0 +1,14 @@
+package nextstep.courses.domain.image;
+
+import nextstep.courses.InvalidImageFileException;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+public class ImageFileExtensionTest {
+    @Test
+    void 이미지_확장자는_gif_jpg_png_svg만_가능하다() {
+        assertThatThrownBy(() -> ImageFileExtension.from("txt"))
+                .isInstanceOf(InvalidImageFileException.class);
+    }
+}
diff --git a/src/test/java/nextstep/courses/domain/image/ImageSizeTest.java b/src/test/java/nextstep/courses/domain/image/ImageSizeTest.java
new file mode 100644
index 000000000..c7afd3a72
--- /dev/null
+++ b/src/test/java/nextstep/courses/domain/image/ImageSizeTest.java
@@ -0,0 +1,14 @@
+package nextstep.courses.domain.image;
+
+import nextstep.courses.InvalidImageFileException;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+public class ImageSizeTest {
+    @Test
+    void 이미지의_크기는_1MB_이하이다() {
+        assertThatThrownBy(() -> new ImageSize(1025))
+                .isInstanceOf(InvalidImageFileException.class);
+    }
+}
diff --git a/src/test/java/nextstep/courses/domain/session/EnrollmentConditionTest.java b/src/test/java/nextstep/courses/domain/session/EnrollmentConditionTest.java
new file mode 100644
index 000000000..a8715a5de
--- /dev/null
+++ b/src/test/java/nextstep/courses/domain/session/EnrollmentConditionTest.java
@@ -0,0 +1,19 @@
+package nextstep.courses.domain.session;
+
+import nextstep.payments.domain.Payment;
+import nextstep.users.domain.NsUserTest;
+import org.junit.jupiter.api.Test;
+
+import static nextstep.courses.domain.session.SessionTest.*;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+public class EnrollmentConditionTest {
+    public static final EnrollmentCondition JAVAJIGI_CONDITION = new EnrollmentCondition(NsUserTest.JAVAJIGI, new Payment(SESSION_ID, NsUserTest.JAVAJIGI.getId(), 30_000L));
+    public static final EnrollmentCondition SANJIGI_CONDITION = new EnrollmentCondition(NsUserTest.SANJIGI, new Payment(SESSION_ID, NsUserTest.SANJIGI.getId(), 30_000L));
+
+    @Test
+    void 수강신청자와_결제자가_서로_다르면_수강신청_조건을_충족하지_않는다() {
+        assertThatThrownBy(() -> new EnrollmentCondition(NsUserTest.JAVAJIGI, new Payment(SESSION_ID, NsUserTest.SANJIGI.getId(), 30_000L)))
+                .isInstanceOf(IllegalArgumentException.class);
+    }
+}
\ No newline at end of file
diff --git a/src/test/java/nextstep/courses/domain/session/SessionEnrollmentTest.java b/src/test/java/nextstep/courses/domain/session/SessionEnrollmentTest.java
new file mode 100644
index 000000000..182666b2b
--- /dev/null
+++ b/src/test/java/nextstep/courses/domain/session/SessionEnrollmentTest.java
@@ -0,0 +1,50 @@
+package nextstep.courses.domain.session;
+
+import nextstep.courses.SessionUnregistrableException;
+import nextstep.courses.domain.image.Image;
+import org.junit.jupiter.api.Test;
+
+import static nextstep.courses.domain.session.EnrollmentConditionTest.JAVAJIGI_CONDITION;
+import static nextstep.courses.domain.session.EnrollmentConditionTest.SANJIGI_CONDITION;
+import static nextstep.courses.domain.session.SessionTest.SESSION_ID;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+class SessionEnrollmentTest {
+    private static final Image IMAGE = new Image(1_024, 300, 200, "png");
+
+    @Test
+    void 강의는_모집중_상태가_아니면_신청할_수_없다() {
+        Session freeSession = Session.createFreeSession("free", IMAGE);
+        SessionEnrollment enrollment = new SessionEnrollment(freeSession);
+        assertThatThrownBy(() -> enrollment.enroll(JAVAJIGI_CONDITION))
+                .isInstanceOf(SessionUnregistrableException.class);
+    }
+
+    @Test
+    void 무료_강의는_인원수_제한없이_들을_수_있다() {
+        Session freeSession = Session.createFreeSession("free", IMAGE);
+        freeSession.openRecruiting();
+        SessionEnrollment enrollment = new SessionEnrollment(freeSession);
+        enrollment.enroll(JAVAJIGI_CONDITION);
+        enrollment.enroll(SANJIGI_CONDITION);
+    }
+
+    @Test
+    void 유료_강의는_인원수_제한이_있다() {
+        Session paidSession = Session.createPaidSession(SESSION_ID, "paid", IMAGE, 30_000L);
+        paidSession.openRecruiting();
+        SessionEnrollment enrollment = new SessionEnrollment(1, paidSession);
+        enrollment.enroll(JAVAJIGI_CONDITION);
+        assertThatThrownBy(() -> enrollment.enroll(SANJIGI_CONDITION))
+                .isInstanceOf(SessionUnregistrableException.class);
+    }
+
+    @Test
+    void 유료_강의는_지불한_금액이_맞아야_한다() {
+        Session paidSession = Session.createPaidSession(SESSION_ID, "paid", IMAGE, 20_000L);
+        paidSession.openRecruiting();
+        SessionEnrollment enrollment = new SessionEnrollment(1, paidSession);
+        assertThatThrownBy(() -> enrollment.enroll(JAVAJIGI_CONDITION))
+                .isInstanceOf(SessionUnregistrableException.class);
+    }
+}
\ No newline at end of file
diff --git a/src/test/java/nextstep/courses/domain/session/SessionTest.java b/src/test/java/nextstep/courses/domain/session/SessionTest.java
new file mode 100644
index 000000000..44d33dd88
--- /dev/null
+++ b/src/test/java/nextstep/courses/domain/session/SessionTest.java
@@ -0,0 +1,32 @@
+package nextstep.courses.domain.session;
+
+import nextstep.courses.domain.image.Image;
+import nextstep.payments.domain.Payment;
+import nextstep.users.domain.NsUserTest;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class SessionTest {
+    public static final Long SESSION_ID = 123L;
+    private static final Image IMAGE = new Image(1_024, 300, 200, "png");
+
+    @Test
+    void 모집중_상태로_변경하면_정상적으로_상태가_변경된다() {
+        Session freeSession = Session.createFreeSession("free", IMAGE);
+        freeSession.openRecruiting();
+        assertThat(freeSession.isRecruiting()).isTrue();
+    }
+
+    @Test
+    void 강의_수강신청_가능_조건을_입력해_수강신청_가능_여부를_확인한다() {
+        Session paidSession = Session.createPaidSession(SESSION_ID, "paid", IMAGE, 20_000L);
+        paidSession.openRecruiting();
+
+        EnrollmentCondition trueCondition = new EnrollmentCondition(NsUserTest.JAVAJIGI, new Payment(SESSION_ID, NsUserTest.JAVAJIGI.getId(), 20_000L));
+        assertThat(paidSession.canEnroll(trueCondition)).isTrue();
+
+        EnrollmentCondition falseCondition = new EnrollmentCondition(NsUserTest.SANJIGI, new Payment(SESSION_ID, NsUserTest.SANJIGI.getId(), 30_000L));
+        assertThat(paidSession.canEnroll(falseCondition)).isFalse();
+    }
+}
\ No newline at end of file
diff --git a/src/test/java/nextstep/courses/domain/session/type/PaidTest.java b/src/test/java/nextstep/courses/domain/session/type/PaidTest.java
new file mode 100644
index 000000000..f6bc11278
--- /dev/null
+++ b/src/test/java/nextstep/courses/domain/session/type/PaidTest.java
@@ -0,0 +1,27 @@
+package nextstep.courses.domain.session.type;
+
+import org.junit.jupiter.api.Test;
+
+import static nextstep.courses.domain.session.SessionTest.SESSION_ID;
+import static nextstep.courses.domain.session.EnrollmentConditionTest.JAVAJIGI_CONDITION;
+import static org.assertj.core.api.Assertions.assertThat;
+
+class PaidTest {
+    @Test
+    void 유료_강의는_수강생이_결제한_금액과_수강료가_일치할_때_수강_신청이_가능하다() {
+        Paid paidSession = new Paid(SESSION_ID, 30_000L);
+        assertThat(paidSession.canEnroll(JAVAJIGI_CONDITION)).isTrue();
+    }
+
+    @Test
+    void 유료_강의는_수강생이_결제한_금액과_수강료가_불일치하면_수강_신청이_불가하다() {
+        Paid paidSession = new Paid(SESSION_ID, 20_000L);
+        assertThat(paidSession.canEnroll(JAVAJIGI_CONDITION)).isFalse();
+    }
+
+    @Test
+    void 유료_강의는_수강생이_결제한_강의와_신청한_강의가_불일치하면_수강_신청이_불가하다() {
+        Paid paidSession = new Paid(SESSION_ID + 1, 20_000L);
+        assertThat(paidSession.canEnroll(JAVAJIGI_CONDITION)).isFalse();
+    }
+}
\ No newline at end of file
diff --git a/src/test/java/nextstep/courses/infrastructure/CourseRepositoryTest.java b/src/test/java/nextstep/courses/infrastructure/CourseRepositoryTest.java
index f087fc0ad..530375d3e 100644
--- a/src/test/java/nextstep/courses/infrastructure/CourseRepositoryTest.java
+++ b/src/test/java/nextstep/courses/infrastructure/CourseRepositoryTest.java
@@ -1,7 +1,7 @@
 package nextstep.courses.infrastructure;
 
-import nextstep.courses.domain.Course;
-import nextstep.courses.domain.CourseRepository;
+import nextstep.courses.domain.course.Course;
+import nextstep.courses.domain.course.CourseRepository;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.slf4j.Logger;