Since the mid-1970s, scientists have called for a unification of the fields of embryo development, genetics, and evolution. Each field has glaring holes in its ability to explain the fundamental phenomena of life. In this book, the author shows how the phenomenon of cell differentiation, considered in its temporal and spatial aspects during embryogenesis, provides a starting point for a unified theory of multicellular organisms, including their evolution and genetics. This unification is based on the recent discovery of differentiation waves by the author and his colleagues, described in the appendices, and illustrated by a flip movie prepared by a medical artist. To help the reader through the many fields covered, a glossary is included.