  I present a brief overview of the wealth of femtoscopic measurements from the
past two decades of heavy ion experiments. Essentially every conceivable knob
at our disposal has been turned; the response of two-particle correlations to
these variations has revealed much about he space-momentum substructure of the
hot source created in the collisions. I discuss the present status of the
femtoscopic program and questions which remain, and point to new efforts which
aim to resolve them.
