Social work, globally, has struggled persistently to justify itself as an academic or professional discipline. Its terrain is not the academic high ground, where principles and concomitant courses of action seem clear, but the domain of practice, where knowledge and actions are plural, ambiguous, situated and contested. A consequence of the diffuse nature of social work knowledge and practice is that workers can struggle to articulate what it is they do by comparison to other professions where knowledge can appear more bounded. In this article, we explore the impact of this on the profession’s identity. The article is structured into three main sections: the first sets out some of social work's struggles with knowledge. We then introduce data from a Scottish study on the challenges social workers face to account for what they do. In the final section, we consider what this insecurity about a coherent knowledge base might mean for workers’ professional identity.