The stability assessment of earth slopes is one of the fundamental calculations in geotechnical engineering. The most commonly used methods for slope stability assessment is based on the limit equilibrium method of slices. In these methods, the potential sliding mass is subdivided into a number of vertical slices. The analysis is based on generation of the trial failure surfaces and evaluation of the safety factor corresponding to each trial surface. The critical failure surface is a surface with the lowest factor of safety. Generally, the problem of locating the critical failure surface associated with the minimum factor of safety may be formulated as an optimization problem and an effective optimization algorithm could provide a reliable solution. In this book, first the available global optimization techniques and limit equilibrium methods of slices will be reviewed. Afterwards, an effective global optimization algorithm based on particle swarm optimization will be presented. Also, application of the new algorithm for slope stability analysis and evaluation of minimum factor of safety and its associated critical failure surface will be discussed in detail.