Results from integral-effects core melt progression experiments and from the examination of the damaged core of the Three Mile Island Unit 2 (TMI-2) reactor are reviewed to gain insight on key severe accident phenomena. The experiments and the TMI-2 accident represent a wide variety of conditions and physical scales, yet several important phenomena appear to be common to core melt progression. Eutectic interactions between core materials cause the formation of liquids and loss of original core geometry at low temperatures (∼1500 K) in a severe accident. The first liquids to form are metallic in nature, and they relocate to lower elevations in the core, where they may freeze into a crust that forms a partial flow blockage. At temperatures above ∼2200 K, fuel liquefaction causes fuel-bearing debris to accumulate in the core above the metallic lower crust. The liquefied material oxidizes in steam as it relocates, and the accumulated melt can incorporate unmelted fuel rod debris. The result is the formation of a molten ceramic pool above the metallic crust. This molten pool can be uncoolable, as was the case in the TMI-2 accident, but failure of the peripheral crust can cause a coherent relocation of core melt to the lower plenum of the reactor and fragmentation of the melt in water to form a coolable debris (as occurred in the TMI-2 accident). Fission product release early in a severe accident is controlled by diffusion through solid fuel and is strongly influenced by microstructural features such as cracks and grain-boundary porosity interlinkage. Cracking due to rapid cooling (e.g., during reflooding) can enhance fission product release, as can liquefaction. Fission product release from the molten pool is controlled by bubble dynamics and the oxygen potential within the pool. Some inventory of volatile fission products, among others, remains in the melt, even after relocation to the lower plenum.