In addition to data collected by observation on 143 days over a 13-month period of residence in a lower and working class neighborhood, formal interviews were conducted with 40 serious thieves, 2 nonthieving peers, 2 professional thieves, and 4 fences. Analysis and cross-checking of observational, interview, and documentary data reveals that the thief's chief form of protection is his ability to pass as an ordinary citizen, thus playing on the trust of the public in those who look and behave normally. Additionally, by avoiding dealing with unknown parties the thief reduces his vulnerability. While the thief conceals his identity and activity from most others, there are others to whom he must signify that he is a thief. In these relationships, trustworthiness is established by ensuring that the others have compromising side-bets. These side-bets which protect against informing include personal gain, the need to maintain a relatively honorable public/community reputation, fear of physical violence/retaliation, and the maintenance of self-justifying motives and rationales which provide an ideological legitimation of theft. Thus, secrecy and trust are essential for the operations of serious thieves who operate within a community, part of which seeks their elimination. Thieves establish a social order with colleagues and others by granting them trust based on mutual gain, vulnerability to coercion, a social community, and ideological commonality. Included are 56 references.