In contrast to the active conformations of protein kinases, which are essentially the same for all kinases, inactive kinase conformations are structurally diverse. Some inactive conformations are, however, observed repeatedly in different kinases, perhaps reflecting an important role in catalysis. In this review, we analyze one of these recurring conformations, first identified in CDK and Src kinases, which turned out to be central to understanding of how kinase domain of the EGF receptor is activated. This mechanism, which involves the stabilization of the active conformation of an α helix, has features in common with mechanisms operative in several other kinases.