Book excerpt: Anti-fascism has long been one of the most active and dynamic areas of radical protest and direct action. Yet it is an area of struggle and popular resistance that remains largely unexplored by historians, sociologists and political scientists. Fully revised and updated from its earlier edition, this book continues to provide the definitive account of anti-fascism in Britain from its roots in the 1930s opposition to Oswald Mosley and the British Union of Fascists, to the street demonstrations and online campaigns of the twenty-first century. The author draws on an impressive range of sources including official government, police and security services records, the writings and recollections of activists themselves, and the publications and propaganda of anti-fascist groups and their opponents. The book traces the ideological, tactical and organisational evolution of anti-fascist groups and explores their often complicated relationships with the mainstream and radical left, as well as assessing their effectiveness in combating the extreme right.