This book answers the question why London has been a stronghold for the Labour Party for relatively long periods of the last century and continues to be so to this day to an extent that surprises contemporaries. The book draws on evidence from history and political sociology as well as the personal experience of the author in London local government during the 1980s. It argues that while changes in the London economy, plus the ability of the party to forge cross-class alliances, can go some way to explain the success of the Labour Party in London, a range of other demographic and social factors need to be taken into account, especially after the year 2000. These include the size of London’s growing black and ethnic minority communities; higher concentrations of well-educated younger people with socially liberal values; the increasing support of the middle-classes; the impact of austerity after 2008; and the degree of poverty in London compared to non-metropolitan areas. This book will be of key interest to readers interested in the history of the Labour Party, the politics of London, Socialist politics/history, British politics/history, government, political sociology, and urban studies.