In the last two decades an increasing number of archaeological least-cost path (LCP) studies have been published. LCP analysis recently has become part of the predictive modelling toolkit in American archaeology. Most archaeologists applying push-button LCP software are not aware of the limitations of Geographical Information Systems (GIS) functions. The chapter shows that standard GIS software lacks some features that are important in archaeological optimal path calculations. The developments of LCP analysis and cost-surface analysis in archaeology are closely connected, because, as mentioned, most LCP methods calculate an accumulated cost surface (ACS) as a first step. Dijkstra's algorithm selects one optimal path in the presence of several alternatives. Batten advocates starting with the simplest model, which, in nigged terrain, is based mainly on slope, and to refine this model if necessary after comparing the paths based on the simple model with the known or expected paths.