Considering solidarity and mutual aid at the intersection of political philosophy and biology, made more urgent and prescient by the COVID-19 crisis, this book is grounded in the work of Catherine Malabou and takes her theories in creative new directions. To think about solidarity mutual aid is to think about how we can and do live together, and how we might do so differently. Mutual aid is, in Peter Kropotkin’s famous formulation, a factor of evolution, but also a conscious political strategy undertaken by activists in times of crisis. While this combination of biology and politics has been a source of controversy, and even embarrassment, recent developments demand a rethink. The contributions in this volume aim to renew interest in the idea of mutual aid, and to consider how biological claims might be incorporated into political projects without appearing as essentialist constraints. They do so in dialogue with Catherine Malabou, whose work insists on the importance of the biological while rejecting any notions of biological determinism. They thus point to the necessity of solidarity and mutual aid for understanding our social life, while releasing them from the biological and symbolic chains in which they often appear.