One focus is the analysis of reforms of the tax system, both ex post using quasi-experimental methods and ex ante using economic models and microsimulation. The RWI income tax microsimulation model and the sales tax model are used to analyze the revenue and distributional effects of tax reforms with respect to public finances. This work provides important contributions to current economic policy discussions. In addition, the continuously extended models can be used to analyze scientifically relevant issues. Extensions relate, in particular, to the simulation of transfers, social security contributions, and social security benefits. In addition, the simulation model is used to improve forecasts of tax revenues (tax estimates).