The study of paleoliquefaction grew out of (1) the recognition that earthquakes left their imprint on soft sediments as deformational structures primarily through liquefaction, and (2) the need for applying paleoseismology to settings in which active faults were not readily recognizable, accessible, or did not reach the surface. Earthquake-induced liquefaction features are distinctive, and their formation is a result of strong ground shaking that may or may not result in lateral spreading. Paleoliquefaction features include sand blows, and intrusive dikes and sills, as well as less prominent, but equally informative features such as load casts, pseudonodules, ball-and-pillow structures, and convolute lamination. Fluvial depositional environments, with generally easy access and relatively abundant natural outcrops, have been the primary choice for conducting paleoseismic studies. In general, when relying on sand dikes and sills, sand blows, and their related structures common in fluvial sediments, one is restricted to river valleys. Depending on the density of the drainage network and the size of the streams, one may not obtain as much data as would be desired. Therefore, other environments that may contain earthquake-induced liquefaction structures may need to be sought out. Lacustrine and paleolacustrine deposits also have a distinctive suite of liquefaction-induced sedimentary structures, most commonly pseudonodules and load casts, and less commonly convolute lamination. However, these structures are not limited to lacustrine deposits, because they have been observed in paleoliquefaction source beds in the New Madrid seismic zone, liquefaction accompanying the 26 January 2001, Bhuj, India, earthquake, and liquefaction associated with the Charlevoix seismic zone. The earliest earthquake-induced paleoliquefaction features were described and correlated to specific earthquakes using soft-sediment deformational structures in lake sediments and a series of modern earthquakes in California, and deformational structures in prehistoric lake sediments. Ancient lake deposits have been used for paleoseismological studies with some success in the United States in California, Oregon, Washington, and Alaska. Such deposits have also been successfully used in Europe and the Middle East. The most promising of these studies have been in varved glaciolacustrine deposits. Varves are small-scale (centimeter to millimeter) sedimentary units. They form in a variety of marine and lacustrine depositional environments from seasonal variation in clastic, biological, and chemical sedimentary processes. The most common seismically induced structures that occur in varved glaciolacustrine deposits are pseudonodules.