This article examines the main ideas presented in Newell's groundbreaking article, published in "Issues in Integrative Studies" in 2001, "A Theory of Interdisciplinary Studies": that complexity is a precondition for interdisciplinary research, that interdisciplinary research utilizes disciplinary perspectives, and that integration of insights drawn from disciplinary perspectives is the goal of interdisciplinary research. It also examines the development of the interdisciplinary research process presented in the article. The controversies surrounding these ideas are explored in depth, along with the overall impact of the article on the field of interdisciplinary studies.