The term ＇＇triangle zone＇＇ was first used informally in 1957 to describe the structure of the east edge of the Foothills thrust belt of the southern Canadian Cordillera. Since then, triangle zones have been recognized at the foreland margins of most of the world＇s thrust-and-fold belts. Variations in terminology of triangle zones reflect differences in interpretation of their internal geometry and their role in orogenesis. The principal issue is whether triangle zone formation occurs only at the final stage of evolution of a thrust belt or is a continuously regenerated tectonic process that creates deformed belts. Evidence is given to support the second interpretation, leading to a hypothetical kinematic model for the formation of thrust-and-fold belts. According to this model, emplacement of successive triangle zones creates a foreland-migrating frontal monocline. Physiographic and structural relief of this structure continuously regenerates a foreland-migrating envelope of overpressured section in the undisturbed foreland sequence ahead of it, causing continued progradation of the deformation front. In some areas gravity sliding takes place down the foreland-facing dip slope of frontal monoclines. The gravity slides themselves may have emergent or buried (triangle zone) thrust fronts.