Boundary conditions of the placer formation environment are discussed on the basis of a comprehensive study of approximately 40 placer-forming minerals and examination of the following features of minerals: stability under different conditions of migration and redeposition; capacity to be concentrated in a certain grain size class; and industrial requirement of the raw mineral quality. It is suggested that the migration capacity of placer-forming minerals is realized in a wide range of conditions. The work discusses specific features of the transformation of placer mineral assemblages during the scattering and relative concentration in local structural-sedimentation traps (denudation cycle) and the absolute concentration and development of new parageneses in terminal sedimentary basins. The role of structural-sedimentation traps in the formation of large and superlarge placers is demonstrated. It is shown that all types of continental lithogenesis are valid for placer formation, although each type can contribute some specific features to the placer-forming process. Five megaepochs of placer formation are identified in the Earth's history. The duration of Phanerozoic megaepochs, except the last (incomplete) one, is approximately 100 Ma. In terms of placer productivity during the Phanerozoic, the second half of the Paleozoic ranks below the Cenozoic megaepoch.