In introducing this second volume on case formulation we thought it worthwhile to revisit some of the stages in the development of case formulation and review and update some of the issues that have been raised. As with all aspects of clinical practice, the process of case formulation – working towards a psychological explanation of a client’s problem – is not static. There remain numerous challenges and no doubt further challenges will arise in the future. To stop and reflect on these issues and the challenges they impose is helpful both to the individual clinician and to the clinical researcher. This is especially true with increasing changes in clinical services brought about by prevailing economic conditions and the accelerating development of new technologies. These factors potentially change the environments within which cognitive behaviour therapy (CBT) is delivered and hence in which case formulation is practiced.