This is the third and fully updated edition of the classic textbook on physics at the subatomic level. An up-to-date and lucid introduction to both particle and nuclear physics, the book is suitable for both experimental and theoretical physics students at the senior undergraduate and beginning graduate levels. Topics are introduced with key experiments and their background, encouraging students to think and empowering them with the capability of doing back-of-the-envelope calculations in a diversity of situations. Earlier important experiments and concepts as well as topics of current interest are covered, with extensive use of photographs and figures to convey principal concepts and show experimental data. This modern edition makes use of Lagrangians rather than Hamiltonians (where appropriate) and greater use of relativistic notations. The coverage includes new material on: detectors and accelerators; nucleon elastic form factor data; neutrinos, their masses and oscillations; chiral theories and effective field theories, and lattice QCD; relativistic heavy ions (RHIC); nuclear structure far from the region of stability; and particle astrophysics and cosmology.