This thesis investigates the nature and the development of a delinquent social identity. Three issues are addressed. These concern the negative identity that results from social comparison processes in school, the role of the peer group in delinquency and the variable nature of the delinquent social identity. One argument of the thesis, which is based on the concepts of self-categorization theory, is that the delinquent social identity develops out of a negative identity because of perceived differences between groups of adolescents in the school in terms of their commitment to academic studies and their attitude towards authority. The first study in this thesis demonstrates that compared to non delinquents, delinquents are more likely to perceive their social status in the school to be low as well as stable, and are more concerned about their reputation among their peers. Also, delinquents are more likely to rationalize against guilt through the techniques of neutralization, are more likely to value unconventional norms and tend to have negative experiences, both at home and in school. Based on social identity theory, this thesis argues that delinquency arises out of a search for an alternative positive identity through " social creativity ", which is only possible through the group. Membership in a delinquent group or a delinquent social identity offers the delinquent a sense of " positive distinctiveness " which is derived from the rejection, redefinition and reversal of conventional norms. It is only through a social identity where members perceive each other as interchangeable and share an interdependency, that such a reversal receives social validation, and that members achieve a sense of self-consistency which becomes part of their reputation. The second study in this thesis confirms that delinquents show a relative preference for a group strategy of derogation of the outgroup for coping with negative social comparison, rather than one which involves an individual strategy of competition, and that this group strategy is more likely to enhance their self-esteem. Delinquents' tendency to reverse conventional norms is demonstrated in the third study of the thesis, which also revealed that this reversal is evident only when delinquents are compared to non delinquents, and that this rejection is not total. These findings not only provide support for Cohen's subcultural theory of delinquency but also that of Sykes and Matza who argue that delinquents drift in and out of such behaviours. In fact, this thesis suggests that this drift can be explained in terms of a shift in the salience of identity. Because the delinquent identity is a social identity, it is variable and context-dependent. Differences in attitudes towards authority, rationalizations against guilt and self-derogation can be explained by differences in the salience of the delinquent social identity. The last three studies of the thesis provide evidence of these variations with both self-report and incarcerated delinquents.