Clinical reasoning is one of the central components of psychological assessment. The identification of a client's psychological difficulties and the subsequent depiction of their onset, development, and interrelationships enables clinicians to plan treatment in a systematic and effective manner. In a recent paper (Ward & Haig, 1997), we presented an abductive theory of method and showed how it offered a useful framework for highlighting and integrating the major phases of psychological assessment. These phases involve detecting clinical phenomena, postulating psychological mechanisms, developing a case formulation, and evaluating a case formulation. In this paper we outline the abductive theory and elaborate on the related clinical dimensions of assessment, while illustrating them with an ongoing case example.