This interdisciplinary project is a response to the need for supporting policy makers in designing and implementing appropriate policies regarding irregular migration.The project aims:(a) to provide an inventory of data and estimates on irregular migration (stocks and flows) in selected EU countries,(b) to analyse these data comparatively,(c) to discuss the ethical and methodological issues involved in the collection of data, the elaboration of estimates and their use,(d) to propose a new method for evaluating data/estimates on irregular migration in the EU.The project will address these aims in selected EU countries (Greece, Italy, Portugal and Spain in southern Europe; Netherlands, UK, Germany and Austria in Western and Central Europe; Poland, Hungary, Slovakia in Central Eastern Europe). It will also look at transit migration in countries/regions used as key "stepping stones" by irregular migrants en route to the EU, notably Turkey, Ukraine and one Maghreb country. Where relevant, the project will consider the factors affecting the shift between legal and undocumented status among migrant populations.The project consortium involves 4 academic partners, one policy institute and one NGO. The first five partners (based in Austria, Britain, Germany, Greece and Poland) will be engaged in empirical and theoretical research for the project in the countries where they are based. They will also select, assign and coordinate the work of national experts based in the other European countries. The project plans include dissemination activities at the local/national level and European level organised by the NGO partner in several among the countries studied.