This Introduction begins by exploring how key production personnel on both Tinker Tailor Soldier Spy (BBC 2, 1979) and Spooks (BBC 1, 2002-11) drew inspiration from the BBC itself when developing a fictionalised version of an intelligence service for the screen,. This is used to frame a brief overview of the histories of British intelligence, broadcasting and spy fiction through the early and mid-20th century, noting numerous intersections and parallels. In particular, it describes the expansion in all three areas in the post-war years, resulting from a complex blend of Cold War paranoia and the growth of an affluent, consumer society. Surveying the book’s methodology, it discusses how this account blends case study analyses with broader examinations of television institutions and British cultural history, in particular considering problems of 'realism' in relation to both the spy genre and British television drama. An overview of the main chapters is provided.