This thesis examines the development and diffusion of a nonn of Corporate Social Responsibility (CSR) in and among British Private Military and Security Companies (PMSCs). Having identified a gap in the literature pertaining to an in-depty analysis of CSR in the PMSC industry the thesis outlines a new analytical model of CSR development and internalisation among PMSCs. The thesis is organised primarily around three case studies and the model forms the framework of analysis applied throughout the case study chapters. Specifically the analysis focuses on a range of socially responsible policies and practices within each PMSC and explores whether, how, why and to what extent CSR had been adopted, developed and internalised and condudes that British PMSCs have undergone considerable change and become increasingly socially responsible.