Part I. Introduction: 1. The birth of elementary particle physics: 1930-1950 Laurie M. Brown and Lillian Hoddeson; Part II. Theoretical Underpinnings: 2. The origin of quantum field theory Paul A. M. Dirac; 3. Growing up with field theory: the development of quantum electrodynamics Victor F. Weisskopf; 4. The development of meson physics in Japan Satio Hayakawa; Part III. Discoveries of Particles: 5. The early stage of cosmic-ray particle research Dmitry Skobeltzyn; 6. Some reminiscences of the early days of cosmic rays H. Victor Neher; 7. Unraveling the particle content of cosmic rays Carl D. Anderson with Herbert L. Anderson; 8. The intriguing history of the ¿ meson Gilberto Bermardini; 9. Some aspects of French physics in the 1930s Pierre V. Auger; 10. The scientific activities of Leprince-Ringuet and his group on cosmic rays: 1933-1953 Louis Leprince-Ringuet; 11. The decay of 'mesotrons' (1939-1943): experimental particle physics in the age of innocence Bruno B. Rossi; 12. Particle physics in the 1930s: a view from Berkeley Robert Serber; 13. The observation of the leptronic nature of the 'mesotron' by Conversi, Pancini and Piccioni Oreste Piccioni; 14. The period that led to the 1946 discovery of the leptronic nature of the 'mesotron' Marcello Conversi; 15. On the discovery of the neutral kaons Robert W. Thompson; Part IV. Discussion and Commentary: 16. First round-table discussion Roger H. Stuewer, Robert W. Seidel, Donald F. Moyer, Victor F. Weisskopf; Gilberto Bernardini, Silvan S. Schweber, Paul A. M. Dirac and Herbert L. Anderson; 17. Second round-table discussion Spencer R. Weart, Takehiko Takabayasi, Satio Hayakawa, Charles Weiner, Bruno B. Rossi, Robert Serber, M. G. K. Menon and Dudley Shapere; 18. Some characteristic aspects of early elementary particle theory in Japan Takehiko Takabayasi; Part V. A New Picture: 19. My work in meso physics with nuclear emulsions Cesare Mansueto Giulio Lattes; 20. The fine structure of hydrogen Willis E. Lamb; 21. Renmormalization theory of quantum electrodynamics: an individual view Julian Schwinger; 22. Two shakers of physics: memorial lecture for Sin-itiro Tomonaga Julian Schwinger; 23. Particle physics in rapid transition: 1947-1952 Robert E. Marshak; Indices.