In this article we evaluate whether the Supreme Court's much-discussed decision in Chevron v Natural Resources Defense Council (1984) signaled a lasting difference in how the justices decide administrative law cases, by comparing and testing the predictions of three distinct theories of Supreme Court behavior. The legal model predicts an increase in deference to administrative agencies. This prediction is shared by the jurisprudential regime model, which also predicts that the justices evaluate key case factors differently before and after Chevron. The attitudinal model predicts no change in the justices’ behavior as a result of Chevron. Although we find that attitudes matter, the fact that we also find support for the legal and jurisprudential regime models undermines the assertion of the attitudinal model that law cannot explain Supreme Court votes on the merits.