This paper presents a non-parametric microsimulation methodology for assessing the determinants of changes in income inequality and poverty. One great advantage of this method over alternatives is that it is not very demanding in terms of modelling labour supply and household behaviour while still providing a plausible link between changes in overall labour market conditions and the full household income distribution. The paper also shows how the method can be adapted to assess the poverty and inequality effects of changes in non-labour incomes (such as through a government transfer programme) and how it can be combined with economy-wide models. Introduction -- Non-parametric microsimulation approach -- Top-down combination of a CGE model and the non-parametric microsimulation method -- An application with a CGE Model for Costa Rica. -- Conclusions -- Appendix A.1: The non-parametric microsimulation methodology step by step -- Appendix A.2: Does path dependence matter? -- Appendix A.3: Additional microsimulation results.