In creatures ranging from birds to fish to wildebeest, we observe the collective and coherent motion of large numbers of organisms, known as 'flocking.' John Toner, one of the founders of the field of active matter, uses the hydrodynamic theory of flocking to explain why a crowd of people can all walk, but not point, in the same direction. Assuming a basic undergraduate-level understanding of statistical mechanics, the text introduces readers to dry active matter and describes the current status of this rapidly developing field. Through the application of powerful techniques from theoretical condensed matter physics, such as hydrodynamic theories, the gradient expansion, and the renormalization group, readers are given the knowledge and tools to explore and understand this exciting field of research. This book will be valuable to graduate students and researchers in physics, mathematics, and biology with an interest in the hydrodynamic theory of flocking.

‘This book presents the seminal work of John Toner on the dynamics of flocks, which started the whole field of active matter. The presentation of these important theoretical results is pedagogical and self-contained and it will be very useful researchers with an interest in active matter.’

Jean-Francois Joanny - Collège de France

‘With this book, John Toner has pulled off the nearly impossible, namely, writing a book that is at once fun, intuitive, inspiring, deep and technical. I particularly loved the ease with which he introduces and explains what it means to write down a hydrodynamic theory, in this case with reference to one of the greatest wonders on the planet, the collective motion of animals.’

Rob Phillips - California Institute of Technology

‘In his characteristic witty style, J. Toner presents in a gentle and pedagogical format the theoretical study that kick-started active matter research. These classical results are complemented by more recent developments that are at the forefront of current research. An essential and pleasurable reading for anyone interested in theoretical active matter.’

Francesco Ginelli - Università degli Studi dell’Insubria