Some of the first analytical tools developed in soil mechanics aimed at evaluating the stability of slopes. In recent years there has been numerous changes proposed on how best to model the behavior of slopes and the mechanisms of instability. “Limit Equilibrium” methods of slices have gone through a series of changes as the computer has provided increased ability to solve complex and nonlinear formulations. In recent years numerous new methods have been proposed for the analysis of slopes. These methods have provided new methodologies for the calculation of the normal forces along any proposed slip surface as well as new search routines that attempt to directly determine the shape and location of the most critical slip surface. Each new method of analysis required testing against a history of experience and previous methods of analysis. Recent developments in the analysis tools used for slope stability have augmented the ability of the practicing engineer to analyze slopes. Three-dimensional (3D) analysis is today easily possible and, therefore, its use in the regulatory environment dominated by 1.3 and 1.5 factors of safety must be understood. The influences of slip shape, new searching methods in 3D, geostrata, loading conditions, anchors, water tables as well as advanced methods of representing surface topology must be considered. How do we now consider the influence of 3D anisotropic bedding planes in rock environments? How do we account for probability? What are new searching methods to determine the slip surface in 3D? How do we determine spatial factors of safety over large land areas? The objective of this paper is to provide the practicing geotechnical engineer with information that allows the assessment of newly proposed methods for determining the factor of safety of soil and rock masses.