This book is a graduate-level self-study guide of bound states in elementary particle physics and consequently in the standard model. The author first recalls the usual quantum electrodynamics (QED) approach to atoms in terms of Feynman diagrams, which assume free states at asymptotic times. Motivated by general principles and data, he then develops a novel method based on a Fock expansion of bound states in temporal gauge. The properties of relativistic bound states are discussed for Dirac states, atoms in motion, QED in D=1+1 dimensions, and hadrons in quantum chromodynamics (including color confinement). This book provides complementary material for quantum field theory courses and is accessible for graduate students and more senior researchers.