This book is conceptualised from a successful course in recent years on cellular biophysics as part of the Masters program in Biophysics at the University of Barcelona. It develops a physical approach to biological processes that aims at a quantitative understanding of fundamental mechanisms and organizational principles behind biological complexity. The focus is on the mechanical aspects at different scales, from molecular force generation to collective cell migration, all treated in a comprehensive and unified manner.It is also self-contained and presents the basic concepts from physics and biology that may complement the different backgrounds of potential students. Whenever possible, the presentation is illustrated with simple quantitative models and many of the examples found are solved explicitly. A collection of additional problems and exercises is also included.