From Academic Rules for PhDs and Research Master’s Degrees.
(Updated February 2011: click link to see most updated version).
A student who desires to attend a course without performing the work of the course must first secure the consent of the instructor. He or she must register in order for the audited course to appear on the transcript; no credit will be received for the audited course. A teaching fellow registered for three course units may register as auditor for one additional course with permission of the graduate group chair.
A student may request that the Doctoral Office change his or her status in a course to auditor, provided that the request is endorsed by the PhD Coordinator in their department and the instructor giving the course and is submitted to the graduate office no later than the end of the second week of the term.
Wharton PhD Students are permitted to AUDIT one course only per term.