This chapter agues for the importance of case studies in generating evidence to guide and/or support policymaking across a variety of fields. Case studies can offer the kind of depth and detail vital to the nuances of context, which may be important in securing effective policies that take account of influences not easily identified in more generalised studies. Case studies can be written in a variety of ways which are overviewed in this chapter, and can also be written with different purposes in mind. At the same time, case studies have limitations, particularly when evidence of causation is sought. Understanding these can help to ensure that case studies are appropriately used to assist in policymaking. This chapter also provides an overview of the types of case studies found in the rest of this volume, and briefly summarises the themes and topics addressed in each of the other chapters.