A general geometric framework underlies the structure, evolution, and mechanical processes associated with thrust faulting. The main purpose of this paper is to review and extend this geometric framework. A certain family of lines must exist where thrust surfaces join along branch lines or end at tip lines. Starting from a description of these lines and individual thrust faults, we examine how they join into thrust systems, either as imbricate fans or duplexes. These thrust systems have distinctive map patterns commonly observed near culminations and windows. Many of the culminations have origins tied in with a particular thrust system. The order in which the fault slices form has a marked effect on the geometry of the thrust system. These systems must be identified to un erstand the provenance of the synorogenic sediments.

Part of a thrust belt may be dominated by one particularly large thrust sheet. In front and beneath these dominant sheets, there is a characteristic sequence of thrust systems with a regular pattern to the involvement of basement.

This overall geometric framework provides new insight into some classic areas, illustrated by a balanced cross section through the Mountain City and Grandfather Mountain windows, in the southern Appalachians and another from the Jura to the Pennines (in the western Alps).