At the 1999 Tampere summit, EU member states committed themselves to developing a comprehensive immigration and asylum policy. Although directives harmonizing border controls or anti-discrimination instruments have been adopted, it remains an incomplete and complex European policy area. This article seeks to explain the timing, form and content of this new domain. It combines the insights of March and Olsen's "garbage can' model with a sociological approach that emphasizes power competition among actors in the same field. Diverse actors have seized upon EU opportunities. Law and order officials in charge of migration control seeking to gain autonomy in intergovernmental settings linked their action to the single market and transnational crime. NGOs providing expertise to Commission units seeking competence in non-economic areas jumped on the "social exclusion' bandwagon by proposing anti-discrimination legislation. These developments - superimposed on policies regarding free movement of workers and services - are thus often contradictory and adhocratic.