This book surveys and lays bare the internal battle in the United Kingdom's Labour party over ideas since the mid-1990s to the present day. It focuses on the leadership periods of Tony Blair, Ed Miliband and Jeremy Corbyn, especially the latter two. They represent the renewal of debating, openly, ideas in the party post-New Labour, as opposed to an almost exclusive focus on electoral, pragmatic, concerns under New Labour. It will highlight these debates, the influential thinkers, advisers, MPs and other critical actors involved. Corbyn, with his spectacular rise to becoming leader, has breathed new life into the left’s ideas and swung the pendulum within the party back towards prioritizing ideology over electoral concerns.