After the appearance of John Tedeschi's groundbreaking work The prosecution of heresy (1971), in recent years several histories of the inquisition in sixteenth-century Italy have been published, including Paolo Simoncelli's Inquisizione romana e riforma in Italia (1988); Adriano Prosperi's Tribunali della coscienza (1996); Christopher Black's The Italian inquisition (2009); and the monumental Dizionario storico dell'Inquisizione (2010). The subject remains a rich field for scholarly investigation, as this most recent contribution shows. Wickersham's book is the first that manages to draw a clear picture of how inquisitors were theoretically equipped to identify the various and often subtle types of heretical behaviour and how they proceeded in the practical exercise of their functions. The author examines the reality of different inquisitorial trials in light of four influential manuals that provided basic instructions to guide the action of inquisitors: the Directorium Inquisitorum, written in 1376 by Nicholas Eymeric, printed in 1503 and then expanded by the Spanish Dominican Francisco Peña; the five-volume Tractatus de haeresi by the jurist Prospero Farinacci (1616); Cesare Carena's Tractatus de Officio Sanctissimae Inquisitionis (1636); and Eliseo Masini's Sacro Arsenale overo Prattica dell'officio della Santa Inquisitione (1621). The examples adduced suggest that inquisitors developed a prosecutorial culture capable of identifying and punishing an elusive crime by joining a well-established intellectual tradition of focusing on ritual practice. Some scholars may have some difficulty in accepting that the study excludes other manuals on heresiology and/or inquisitorial procedure whose knowledge might provide a different narrative, such as Alfonso de Castro's particularly well-received Adversus omnes haereses that went through twenty-six printings between 1534 and 1578. This criticism about reception aside, Wickersham's enviable examination of primary and printed sources is fully successful. It is comforting to know that there was some logic in such an illogical flaw-laden institution.