The eastward enlargement of the European Union will be the fifth enlargement since establishing the European Community in 1957. This paper gives an overview of the most recent undertakings to estimate the costs and benefits of EU enlargement in the framework of model analysis. This field of research is relatively young. Therefore only a few model simulations have been made so far. They can be classified into world models covering several world regions, and in single country models. In both cases, one finds computable general equilibrium - CGE - models as well as macro models. The major findings of world models are that the CE-ECs will be the winners whereas the EU incumbents can expect only small gains from enlargement. Taking into account the costs of enlargement the big question, is how the int e-gration gains are distributed among EU incumbents. As a rule, those countries will benefit the most which have already strong trade relations with the CEECs. In the case of the single country models, Austria is one of those countries with the longest tradition in making model simulations in the case of enlargement. A comparison of CGE model approaches with macro model simulations for Austria shows that the benefits of EU enlargement may be lower than those of the opening-up of Eastern Europe since 1989. (author's abstract) / Series: EI Working Papers / Europainstitut