We review recent models of the internal structure of Pluto and Charon made possible by analysis of the Pluto/Charon mutual events. At a mean density of just over 2 g cm-3 and a predicted rock mass fraction of roughly 0.7, the Pluto/Charon system is significantly rockier than the icy satellites of the giant planets, a contrast which may reflect its formation in a CO-rich outer solar nebula rather than a circumplanetary nebula. Pluto and Charon may in fact be o rocky that they lost volatiles early in their history (possibly during a Charon-forming impact event), although this is still an open issue. Finally, we review the outlook for future study of the Pluto and Charon interiors. ¿ American Geophysical Union 1989