This article examines the United Kingdom’s Department for International Development’s understanding of the correlations between security and development at the policy level, and contrasts this with on-the-ground experiences in Sierra Leone. Drawing on fieldwork from Sierra Leone, the article shows how DFID policy appears to have taken the correlation between security and development for granted. As the lead international actor implementing Sierra Leone’s security sector reform programme, DFID relies upon the validity of the security–development nexus to justify time, money, and expertise spent on issues of security. The relationship between these phenomena is presented as commonsensical and uncontested, but the specific nature of the relationship has been glossed over, with little real empirical evidence to demonstrate nexus claims. In Sierra Leone newfound security has so far failed to produce the anticipated development, suggesting that the causal link between security and development may not be as straightforward as implied. The article concludes that more precise investigations of the manner in which security and development interact in practice are needed.