Published by the American Geophysical Union as part of the Field Trip Guidebooks Series, Volume 380.Fold-thrust belts have many attributes in common, but some of the important attributes vary greatly. The purpose of this field trip is to examine the range of variation of several important attributes of fold-thrust belts, including (1) the tectonic setting of deposition of the allochthonous sedimentary rocks, (2) the presence or absence of crystalline basement rocks in the allochthon, (3) the stratigraphic level of the basal decollement, (4) the geometry and internal structure of thrust sheets, and (5) the effects of basement structures beneath the allochthon on the geometry and kinematics of the fold-thrust belt. Four regions in North American fold-thrust belts (Fig. 1-1) are visited on this field trip to examine the range of variation in the listed attributes. The four regions are (1) the Alabama Appalachians (the southernmost exposures of the Appalachian orogen), (2) the Ouachitas (exposures in the Ouachita Mountains in Arkansas and Oklahoma), (3) the Idaho-Wyoming Rockies (exposures of the Cordilleran fold-thrust belt), and (4) the Montana Rockies (exposures of the frontal part of the Cordilleran fold-thrust belt and basement structures of the Rocky Mountain foreland).