Studies using sediment traps in lakes reveal that the seasonal flux of sediment regulates both the composition and timing of deposition of materials that reach the bottoms of lakes. If the bottom waters of a lake are partly or totally anoxic, the seasonally deposited materials are preserved as annual groupings of laminae (varves). Common components that form individual laminae consist of allochthonous clastic material derived from the drainage basin, precipitated carbonate minerals, diatom frustules, iron-rich and manganese-rich flocs, autochthonous organic detritus, and autochthonous and allochthonous materials resuspended from the bottom. The "style" of varving has changed over geologic time, reflecting changes in biologic evolution and types of materials available. Precipitated iron-rich laminations were common in the middle Precambrian. Graded sets of clastic organic laminations persisted through the Precambrian, prior to the evolution of bioturbating benthic organisms. Glaciolacustrine varves appear to have retained their distinctive character through time. Carbonate-rich varves occurred sporadically in the Precambrian and Phanerozoic. With the exception of diatoms, major components of modern lacustrine varves were present through the Paleozoic and Mesozoic, and yet varves are rare in strata of these ages, and may have accumulated in marine to brackish-water environments. Diatoms were introduced into lacustrine systems in Early Tertiary time and are common components of varves from then on. Diatom laminae, combined with a greater chance for geologic preservation of younger lake deposits, have increased the number of geologically young occurrences of varved sediments. However, seasonal associations of modern varve components, and the processes they represent, are present in ancient deposits and provide clues to the interpretation of ancient environments. ?? 1988.