Dr. Jody R. Rosen and I wrote this article to argue that the kinds of undergraduate research (UR) opportunities most useful to students at HSIs and MSIs are offered through an across-the-curriculum (ATC) approach. We define an ATC approach to UR as inclusive of traditional UR and broading participation in research through informal research activities at all levels of curriculum and without special facilities, that employ experiential, problem-based skills and practices.