If the course is set up for “Instructor Permission” through the registration system, you will find notice of this under Registration Notes. In this case, there is an envelope icon that allows you to send an email request to enroll. The instructor will respond within the registration system.
Some courses however, have other application or preregistration requirements. Review the Class Notes or Course Description in Yale Course Search and the expanded course description in Canvas. Courses that utilize the Preference Selection system, which opens prior to registration, are listed on the Preference Selection website. You may also review the website of the department offering the course.