This page lists popular pre-approved electives for the HCI major and minor. This list is not exhaustive and there are many other accepted electives university-wide.
The HCI major and minor require four 9-unit (or more) electives, which need to be approved by the HCI undergraduate program director. Other courses may be approved as well, provided that they have HCI-relevant content and extend what the student would do in their primary major (for this reason, basic courses in the student's primary major typically are not approved as electives). Undergraduate students in the HCI programs must submit all electives through EASY, the HCII's internal academic audit system http://easy.hcii.cs.cmu.edu/easy). The general rules on HCI electives are 1. They need to be HCI relevant and 2. If offered in your primary major’s department they need to be 300-level or higher.
Even if a course has a graduate number, it can be used as an undergraduate elective if is open to undergraduate students.