Index: iknow-api/DTOs/EnrollmentDTO.cs
===================================================================
--- iknow-api/DTOs/EnrollmentDTO.cs	(revision ea405569ef29f56fbfc4d77708b6b3faf9286097)
+++ iknow-api/DTOs/EnrollmentDTO.cs	(revision ea405569ef29f56fbfc4d77708b6b3faf9286097)
@@ -0,0 +1,57 @@
+namespace iknow_api.DTOs
+{
+    /// <summary>Everything the enrolment form needs to render.</summary>
+    public class EnrollmentOptionsDto
+    {
+        /// <summary>How many subjects an enrolment must contain.</summary>
+        public int RequiredSubjects { get; set; }
+
+        /// <summary>Semesters this student has not enrolled in yet.</summary>
+        public List<SemesterOptionDto> Semesters { get; set; } = new();
+
+        public List<MajorOptionDto> Majors { get; set; } = new();
+
+        /// <summary>The major from the most recent enrolment, if there is one.</summary>
+        public int? DefaultMajorId { get; set; }
+    }
+
+    public class SemesterOptionDto
+    {
+        public int Id { get; set; }
+        public string? Name { get; set; }
+        public int Year { get; set; }
+        public string? Type { get; set; }
+    }
+
+    public class MajorOptionDto
+    {
+        public int Id { get; set; }
+        public string? Name { get; set; }
+        public List<SubjectOptionDto> Subjects { get; set; } = new();
+    }
+
+    public class SubjectOptionDto
+    {
+        public int Id { get; set; }
+        public string? Name { get; set; }
+        public string? Code { get; set; }
+        public int Credits { get; set; }
+        public int MandatorySemester { get; set; }
+        /// <summary>True when the student already passed this subject.</summary>
+        public bool AlreadyPassed { get; set; }
+    }
+
+    public class EnrollSemesterRequestDto
+    {
+        public int SemesterId { get; set; }
+        public int MajorId { get; set; }
+        public List<int> SubjectIds { get; set; } = new();
+    }
+
+    public class EnrollSemesterResultDto
+    {
+        public bool Ok { get; set; }
+        public string? Message { get; set; }
+        public int? EnrolledSemesterId { get; set; }
+    }
+}