The purpose of this review is to offer a wide-ranging discussion of what causes violent extremism and how it develops and persists. Discussion of violent extremism is often fraught with assumptions and received wisdom that can potentially obscure underlying causes, with implications for government interventions and policy. This review therefore provides an independent critical analysis of the substantial academic literature on what causes violent extremism. The review examines the 17 hypotheses discussed in the 2008 DFID Paper titled ‘Drivers of Violent Extremism: Hypotheses and Evidence’ and discusses their validity. As the scope of these hypotheses is broad, each topic covers a significant quantity of literature. The review is therefore necessarily selective rather than exhaustive, but aims to summarises the most important and credible academic literature, both in support of and against the hypothesis. The review is structured in sections for each hypothesis, preceded by an overall analytical assessment. Following the structure of the 2008 paper, each section includes implications for DFID or HMG in general, but also indicates topics for further research.