Using recently declassified files of the British Security Service (MI5), this dissertation studies agent operations in Britain during the interwar period. 'Tradecraft' -the skills behind the recruitment and handling of agents-was just as important to successful agent operations in the years 1919-1940 as it is today. At times, the quality of tradecraft directly influenced larger policy and security concerns, as this dissertation's analysis of a series of case studies demonstrates. The absence of a rigorous study of clandestine human intelligence (HUMINT) tradecraft in the existing literature of the interwar period-even within the specialised field of intelligence history-is therefore all the more conspicuous. This dissertation is a step towards filling that gap in the historiography of intelligence and interwar Britain.