In this interview, Clarence Allen discusses growing up in southern California; his early interest in science and the outdoors; and his wartime career as a navigator in the Army Air Corps. He recalls his years as a California Institute of Technology (Caltech) graduate student and his thesis work on the San Andreas fault; his work on glaciology with Robert P. Sharp; his growing interest in seismology; and his work with Charles Richter, Hugo Benioff, and Beno Gutenberg in Caltech's Seismological Laboratory. He discusses the interplay at the Seismo Lab in the 1950s between Richter and Gutenberg; the changes wrought by the advent of Frank Press as director in 1957; and the work of Kerry Sieh in paleoseismology. Praise for the division chairmanship (1952-1968) of Robert Sharp. Comments on the "science" of earthquake predicition and failed prediction efforts by the Russians and Chinese. The rise of Caltech to public prominence in the area of seismology. He discusses his own work on earthquake faults as they bear on the assessment of seismic hazards and notes the usefulness of probabilistic analysis in long-term planning to avoid earthquake damage.