This paper presents a review of different elasto-plastic Boundary Element (BE) formulations \\ith particular emphasis on two main approaches; the initial strain displaccmcnt-gradient approach with its modeling of the partial or full interior domain, and the particular integral approach which can be applied exclusively to the surface avoiding any modeling interior. The initial strain formulation is implemcntcd in a computer program using two-dimensional isoparametric quatratic elements to discretise either the complete intcrior domain or only the part associated with the plastic region. The BE solutions are shown to bc in good agreement with analytical and Finite Elcment (FE) solutions.The Boundary Element (BE) method is well established as an accurate numerical tool particularly well suited for linear elastic problems. Its extension to non-linear analysis such as elasto-plasticity, however, is not widespread and in many formulation the interior of the solution domain has to be discretized, thus losing the main BE advantage of surfaceonly modeling.An outline of different elasto-plastic BE formulation is presented in this paper with particular emphasis on two main approaches; (i) the initial strain displacement-gradient approach in which interior discretization is required either for whole domain or only in the region of expected plastic behaviour, and (ii) the particular integral approach in which interior modeling is not required and can be applied exclusively to the surface The analytical and numerical implementation of both approaches are presented. Details of a quadratic BE formulation for the displacement-gradient approach are presented for two-dimensional elasto-plastic problems in which three-node isoparametric quadratic elements are used to model boundary and eight-node isoparametric quadrilateral quadratic elements are used to model the interior domain. The values of stress and strain rates at interior nodes are calculated via the numerical differentiation of the displacement rates in an element-wise manner; an approach similar to that used in FE formulation. Details of the numerical implementation algorithm which uses load incrementation and an iterative procedure are presented To asses the accuracy of the BE formulation, the initial strain displacement-gradient BE formulation is implemented in a computer program and applied to some practical problems. The problems include a square subjected to uniform tension, and a thick cylinder under internal pressure. The BE solutions are compared with the corresponding FE solutions and exact or experimental solutions.The first elasto-plastic BE formulation presented by Swedlow and Cruse [1] was based on a direct analytical formulation.Riccardella [2] presented the initial strain formulation based