Biological physics, the application of physics to provide an understanding of biological phenomenas, is a burgeoning, new inter-disciplinary subject. This text explores the physics behind the architecture of a cell's envelope and internal scaffolding, as well as the properties of its soft components. The analysis is performed within a consistent mathematical framework, although readers can navigate from the introductory material to biological applications without working through the intervening mathematics. The book includes applications and extensions handled through problems at the end of each chapter. This text is aimed at senior undergraduates and graduate students in science and biomedical engineering.