Per the Registrar's Web site:Auditing a Course:
Permission to audit a course entitles the student to attend class but not to hand in papers, take part in discussion, or receive evaluations. An auditor does not receive University credit for the course audited. A law student may not audit a law course.
A University student who wishes to audit a course should obtain a Class Auditor Permit from the Office of the Registrar and secure the consent of the course instructor and the student's dean. A nonstudent must obtain the Class Auditor Permit and the consent of the instructor. Nonstudents under the age of sixty-five are charged an audit fee of $20 a course.
Auditors are permitted only when space is available. An instructor or dean may refuse any request to audit a course. Nothing in these rules prohibits an instructor from permitting guests and visitors in a class.