This interview discusses Fastie's career as a physicist, beginning with a position as research assistant at the Johns Hopkins University Physics Department (1941-45), as a research physicist at Leeds and Northrop (1945-51) and later as a research contract director and research scientist at Johns Hopkins (1951-68). After covering his family background and education, the discussion details Fastie's contact with A.H. Pfund and R.W. Wood, including many anecdotal recollections regarding the classified work of Pfund and Wood during WWII; and his interest in instrumentation as reflected in his work with Echelle gratings and spectrographs. Other topics discussed include: Baltimore city during 1920s; undergraduate and graduate studies at Johns Hopkins University; physical optics; spectrum analysis; infrared gas analysis; pyrometry; Eschelle gratings; Leeds and Northrup; Applied Physics Laboratory (APL); National Defense Research Committee (NDRC); John Sanderson; J.A. Bearden; John Charles Hubbard; G.H. Dieke; John Strong; and George Harrison, among others.