The starting point for this paper is the view that social work practice is a highly skilled activity and that calls for an extensive knowledge base and considerable intellectual abilities. However, considerable confusion remains about what constitutes the knowledge base of social work and how this can be applied to the dilemmas regularly encountered in direct work. This article begins with an account of key writing on the subject of knowledge and, drawing on these works, it describes a framework that includes three interweaving features: (i) theoretical knowledge (or theory); (ii) factual knowledge (including research); and (iii) practice/ practical/ personal knowledge demonstrated by social workers, other professionals and involved individuals. Since most of the published works on the subject of social work knowledge tend to be written by academics, a central aim of this paper is to make this subject accessible to social work practitioners, students, service users and carers in order to encourage their contribution to the debate on what constitutes the knowledge base of social work.