The boundaries between the history of science and science and technology studies (STS) can be misleadingly drawn, to the detriment of both fields. This essay stresses their commonalities and potential for valuable synergy. The evolution of the two fields has been characterized by lively interchange and boundary crossing, with leading scholars functioning easily on both sides of the past/present divide. Disciplines, it is argued, are best regarded as training grounds for asking particular kinds of questions, using particular clusters of methods. Viewed in this way, history of science and STS are notable for their shared approaches to disciplining. The essay concludes with a concrete example--regulatory science--showing how a topic such as this can be productively studied with methods that contradict any alleged disciplinary divide between historical and contemporary studies of science.