 Thomas Polger’s and Lawrence Shapiro’s The Multiple Realization Book (2016) provided what the increasingly fragmenting literature on multiple realizability needed. It is the first book-length treatment of the topic, including many of the broader arguments the topic had become part of. The book pulls together much of the history of work on the topic, plus the more recent work by both proponents and opponents, and usefully organizes all of this around numerous key themes that had come to frame the myriad debates. Polger’s and Shapiro’s goal is not simply to review or clarify the various positions, however. They have a position to push. They end up developing and defending a mind-brain identity theory that explicitly recognizes a sense of the autonomy of psychology from neuroscience. And as one might expect, critics of their view quickly responded. The unifying focus that this book offers, and its initial critical reception, make a detailed discussion of it a useful focus for where the broader issues about multiple realizability stand now, at the end of the second decade of the twentieth century.