In many western societies today the optimism of the 1990s and early 2000s has given way to a deep unease and sense of foreboding. In the aftermath of the financial crisis, many people feel worse off and the future seems bleak. The mood has changed - that's clear. But what is 'the mood'? How can feelings be shared by many people, and how do these shared feelings shape the course of events? In this book, the sociologist Heinz Bude offers a highly original analysis of this vital but neglected topic. Moods, he argues, are ways of being in the world. Moods shape how we experience the world, which feelings and thoughts suggest themselves to us and which are excluded. But moods are not purely private: on the contrary, they form the basic tone or colouring of our collective existence and experience. They are crucial in determining our political outlook and preferences, our attitudes and identities, and they provide much of the energy that underlies forms of collective action, including social movements that seem to appear suddenly from nowhere. With the growing significance of a politics of discontent, Bude's insightful analysis of the power of collective moods could not be more relevant. His book will appeal to anyone wanting to understand how our societies are changing in these profoundly uncertain times.