A captivating exploration of the changing definitions of life in biology Biological Motion studies the foundational relationship between motion and life. To answer the question, "What is Life?," prize-winning historian of science Janina Wellmann engages in a transdisciplinary investigation of motion as the most profound definition of living existence. For decades, information and structure have dominated the historiography of the life sciences with its prevailing focus on DNA structure and function. Now more than ever, motion is a crucial theme of basic biological research. Tracing motion from Aristotle's animal soul to molecular motors, and from medical soft robotics to mathematical analysis, Wellmann locates biological motion at the intersection of knowledge domains and scientific and cultural practices. She offers signposts to mark the sites where researchers, technologies, ideas, and practices opened up new paths in the constitution of the phenomenon of motion. An ambitious rethinking of the life sciences, Biological Motion uncovers the secret life of movement and offers a new account of what it means to be alive.