Slater leaves Harvard University for Massachusetts Institute of Technology (MIT) in 1930 (Karl Compton) to build up Physics Department there; work on quantum electrodynamics. Growth of MIT Physics Department in the 1930s and 1940s, relations between experimentalists and theorists; discussion of works and publications during the 1930s. Changes in U.S. physics; overview of post-World War II physics to 1951, and reasons for establishing own research group; establishment of the Radiation Lab, 1940; magnetron work; Bell Labs visits, 1941-1942 and 1943-1945. Planning of postwar development in MIT Physics Department; transition from Radiation Lab to Research Lab of Electronics; formation of laboratories of nuclear science, acoustics, and spectroscopy; the Lincoln Laboratory, the Instrumental Lab; growth of nuclear branch of Physics Department; physics activity in general in postwar years, Solid State and Molecular Theory Group; the Compton Lab.; Materials Science Center established ca. 1958; interdepartmental and interdisciplinary work; visits to Brookhaven National Laboratory; Slater and Per Olov Lw̲din's Florida Group. Also prominently mentioned are: John Bardeen, W. Buechner, Arthur Holly Compton, Edward Uhler Condon, Jens Dahl, Robley Dunglison Evans, James Brown Fisk, George Harrison, Douglas Rayner Hartree, Raymond George Herb, Milton Stanley Livingston, Millard Manning, Jacob Millman, Wayne B. Nottingham, Isidor Isaac Rabi, Schafer, William Shockley, R. A. Smith, Julius Stratton, Robert Jamison Van de Graaff, John Hasbrouck Van Vleck, Eugene Paul Wigner; American Physical Society, California Institute of Technology, Florida State University, Lawrence Radiation Laboratory, Princeton University, University of Bristol, University of California at Berkeley, and University of Chicago.