Trishear is a kinematic model of fault-propagation folding in which the decrease in displacement along the fault is accommodated by deformation in a triangular shear zone radiating from the tip line. This model has garnered increasing acceptance, particularly for cases where parallel kink-fold models do not work (e.g., footwall synclines, lateral and vertical changes in bedding thickness, and orientation). The articulation of the model in terms of velocity fields has enabled systematic explorations of the parameters controlling the trishear geometry; rapid, objective application of trishear to the simulation of real structures; and application of the model in three dimensions. The model has highlighted the importance of a parameter not unique to trishear, the propagation to slip ratio, which has a profound effect on fold geometry and is fundamental to understanding all types of fault-related folds. The drive to understand the significance of such parameters has instigated the application of several mechanical modeling strategies. Block-motion viscous, finite-element, and discrete-element analyses have all provided insight into trishearlike fault-propagation folds. Clearly, from these models, trishear most successfully simulates fold geometries where significant layered anisotropy is absent and the material is incompressible. Despite these modeling efforts, the significance of the trishear apical angle remains elusive. Trishear has been applied to a variety of real-world problems, including growth strata analysis, potential fracture distribution, paleoseismology, and even seismic hazard analysis.