The discussion of theory develops the perspective that some major ways in which people differ are in the areas of self-image, self-presentational tactics, reference groups, interpersonal sensitivity, and interpersonal competence. These are the principal areas of personality development where criminals differ from law abiding citizens. Personality development occurs in three broad phases. The first phase involves coming to terms with authority and results in the formation of character structure. The second phase involves adjusting to peer group expectations and results in the formation of role structure. The third phase entails forming occupational and career plans and results in the development of a lifestyle. From this conceptual base four conclusions can be drawn about criminal conduct: (1) working class criminals typically experience less than optimal conditions during the first two phases of development, which increase the probability of their choosing a criminal career in the third phase; (2) a tough, defiant, rebellious interpersonal style combined with a poor education facilitates transition to a criminal career; (3) within the population of those with a criminal identity, there is the same status hierarchy found in any human group; and (4) given that some criminal careers are more successful than others, it is difficult to specify precisely how criminals will differ from noncriminals in their self-presentational styles. These principles are confirmed through data obtained from personality measures applied to 57 convicted felons on probation and parole. Tabular data and 40 references are provided.