This work is about the inner structure of everything, a quest which, like the quest for an understanding of the universe at large, goes back to the Ancient Greeks and touches all scientific and philosophical thought since then. Historical highlights include Newton's work on particles and Maxwell's work on waves. The longer biographies in the book include Rutherford, Feynman, Crick and Watson. An extended introduction, which sets out the present state of knowledge, is followed by the main A to Z section, and then by Timelines to indicate what was discovered when.