The aim of this book is to examine the reasons why Communists in German cities during the closing years of the Weimar Republic engaged in a highly organized and often brutal form of gang warfare with their political opponents, usually the National Socialists. I have tried to show how it was possible that members of the Communist movement should have taken up such activities, and how the vigour and tenacity with which they carried on their ‘battle for the streets’ became a source of discord within the movement. When I began my research on this theme, as a graduate student in Cambridge, it was because I was interested in ‘political violence’ as such and its causes. It should be apparent that the book in its present form is very much a study in the history of the German Communist Party (KPD). I am convinced that such a shift of focus must arise inevitably from the nature of the question, once it is recognized that ‘collective violence’ and especially that kind that is known explicitly as ‘political violence’ is simply one of a number of possible forms of political action. Politics, so a leading British politician has recently declared, is for people. What is more certain is that politics is what people do for and about each other, and what people say they are doing. And in the last century it has been the parties of the working-class movement and their organized opponents who have provided the language and arguments in terms of which popular politics has been carried on in Europe.