Studying Charles Tilly (1929–2008), American sociologist, historian and political scientist, is essential for understanding political change and social conflict. His research focuses on how grassroots populations, through different forms of collective action, influence historical events by trying to improve the conditions of people's lives. This book is not only an homage to Tilly, but is also aimed at understanding and applying his thought. In each chapter, the authors, experts on Tilly's work, examine his concepts, theories, and methodological contributions, providing a richer understanding of them. In addition, this book is very contemporary. From the beginning of this century, mainly from 2011, important popular mobilizations, such as the Arab Spring and 15-M or “los indignados” (the indignant movement in Spain), gradually spread to other countries (the US, Yemen, Israel, etc.) in successive “Occupy” movements. The political mobilization of the grassroots movements are undergoing a resurgence, a process that Tilly would have wanted to study. This book can be a good guide for analyzing and understanding these movements.