A fold and thrust belt (FTB) is a series of mountainous foothills adjacent to an orogenic belt, which forms due to contractional tectonics. Fold and thrust belts commonly form in the forelands adjacent to major orogens as deformation propagates outwards. Fold and thrust belts usually comprise both folds and thrust faults, commonly interrelated. They are commonly also known as thrust-and-fold belts, or simply thrust-fold belts.