One of the most widely debated and influential implications of the “demise” of positivism was the realization, now a commonplace, that philosophy of science must be firmly grounded in an understanding of the history of science, and/or of contemporary scientific practice. While the nature of this alliance is still a matter of uneasy negotiation, the principle that philosophical analysis must engage “real” science has transformed philosophical practice in innumerable ways. For one thing, it has led to a systematic questioning, indeed, in the view of many, the dismantling, of “unity” theses and the presumption that the sciences embody a common rational core that philosophers can reasonably expect to “reconstruct.” As HPS practitioners have scrutinized particular sciences, their diversity has come more clearly into focus and this has generated, in turn, vigorous programs of research that take an increasingly wide range of “special” sciences—including various life sciences, earth sciences, and social sciences—as a legitimate primary focus of concern.