Förster's resonance excitation transfer theory: not just a formula

After 65 years of increasing scrutiny and application, Theodor Forster's treatment of resonance excitation transfer is widely quoted and has acquired the acronym FRET, in which "F" originally and rather curiously stood for "fluorescence." In this brief and mostly qualitative survey, we review some of its history, mention its important limitations, and relate some personal encounters with Forster.