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Strike-slip fault systems are major tectonic features at the present day. Some form plate boundaries and some are long-lived fundamental faults which may be related to megashears whose history goes back to early Precambrian times. On a regional scale strike-slip systems may have been subjected to periods of transtension (divergent strike-slip) or transpression (convergent strike-slip). On a local scale curvature, braiding and side-stepping of faults result in contemporaneous formation of closely spaced zones of extension and compression. The main effect of strike-slip motion on sedimentation occurs when dip-slip motion causes rapid sinking of sedimentary basins and uplift and erosion of mountains. Sedimentary facies are therefore very varied, both laterally and vertically, but lateral migration of facies is limited. Ancient strike-slip belts may be recognized by (1) lateral matching of displaced palaeogeographies across faults (2) discordance between size and materials of alluvial fans and possible source areas (3) thick, but not laterally extensive, sedimentary piles deposited very rapidly (4) localized uplift and erosion giving rise to unconformities of the same age as thick sedimentary fills nearby (5) extreme lateral facies variations (6) simultaneous development of both extensional and compressional tectonics within the same tectonic belt (7) a wrench fault style of structural deformation, in particular en echelon folds (8) little or no metamorphism (9) sparse igneous activity, except locally in zones of transtension. The strike-slip cycle of transtension→basin filling→transpression without large oceans or subduction is an alternative to the Wilson cycle of sea-floor spreading→subduction→continental collision to explain the classic geosynclinal cycle of pre-flysch→flysch→molasse. Strike-slip motion may have been important during the Upper Palaeozoic in western Europe and eastern North America and during the development of much of the Caledonides. It can provide ideal conditions for the occurrences of hydrocarbons, economically significant lacustrine deposits, and mineralization.