This book gives a simplified account of a new fundamental theory of physics. It is based on two postulates (or laws) and from these are derived a set of Field Equations. The solutions of these equations account for many of the features of modern physics. These solutions lead to the prediction of Newton's laws of motion and gravitation, Coulomb's law and electromagnetism, and the prediction of the values of the gravitational constant and the charge on the electron which are close to the measured values. They also lead to a formula for Plank's constant, and to Schrӧdinger's equation and the basis for quantum mechanics. Particles are not points. Structures are proposed for the proton, neutron, electron, electron neutrino, muon, pion and kaons. The theory provides an account of the up, down, strange, charm and bottom quarks and the W^± and Z particles. The book is mathematical, but simplified as much as possible to make the book accessible to a wide range of readers.