Power-belief theory introduces an innovative perspective on female criminality, providing important insights into the unique experiences and treatment needs of female offenders. The theory asserts that criminality can best be understood within the context of oppression in patriarchal societies. It is not a female-specific theory. However, it suggests the appropriateness of a gendered theoretical approach, and the focus of this chapter is on female offenders. The chapter begins by presenting evidence that the traditional targets of oppression in patriarchal societies, women and children, occupy uniquely powerless places in the social order. It continues with an outline of some fundamental propositions of the dynamics of oppression, and provides a presentation of the matrices of beliefs that are suggested as most likely to be found among populations of female offenders. The chapter concludes with a brief look at some theoretical and empirical implications of the power-belief theory and a discussion of some of its practical ramifications of treatment for females involved in the adult criminal and juvenile justice systems. The fundamental assertion of power-belief theory presented is that female criminality can best be understood within the context of the dynamics of oppression in patriarchal societies in which both sex and age are key organizing principles of the hierarchical order of power. Table, notes, and references