Interview with William Herrmannsfeldt, Staff Physicist at SLAC. Herrmannsfeldt recounts his German heritage, his upbringing in Ohio, and his early interests in physics which he pursued as an undergraduate at Miami University. He discusses his graduate work on beta decay and nuclear physics at the University of Illinois, under the direction of James Allen, and he describes his postdoctoral appointment at Los Alamos where he made detectors for bomb tests. Herrmannsfeldt explains the connection between his work at Los Alamos on electron optics and his initial research at SLAC, and he describes his work on linear accelerators. He describes his tenure as Secretary of the Advanced Development Group and his role at the AEC to concentrate on accelerator physics for Fermilab. Herrmannsfeldt explains the decision to move ahead with the PEP project and his LINAC work at Berkeley. Herrmannsfeldt explains the relevance of this research to nuclear fusion, and he describes some of the technical challenges in building the superconducting RF system. At the end of the interview, Herrmannsfeldt conveys the sense of fun he felt in learning new technological systems, the inherent challenges of beam dynamics, and he reflects on how SLAC has changed since its inception.