Simulation optimisation is an interesting and fast-growing research field fostered by advances in computer technology and increased computing power. These advances have made it possible to solve complex stochastic optimisation problems using simulation. Most simulation optimisation studies focus on single-objective simulation optimisation (SOSO), and multi-objective simulation optimisation (MOSO) has only recently drawn attention. This paper provides an overview of recent studies on discrete MOSO problems. We surveyed various MOSO algorithms and classified them, based on: 1) the size of the feasible solution space; 2) the method of dealing with the multiple objectives. For the latter, we identified three categories, namely scalarisation methods, the constraint approach, and the Pareto approach. MOSO algorithms in each category are discussed in some detail. We conclude the paper by discussing some related issues in MOSO, which include noise handling techniques and the issue of exploration versus exploitation.