The article introduces constructivist approaches to research on European in
tegration. While stressing middle-range theory, it recognizes that meta-the
oretical choices also matter for theorizing and analysing European integrat
ion. Tracing developments in the philosophy of science and in international
relations theory, social constructivism is introduced as a way of establis
hing the 'middle ground' in juxtaposition to rationalism and reflectivism -
not as a grand theory for the study of European integration. Crucial aspec
ts of the integration process - polity formation through rules and norms, t
he transformation of identities, the role of ideas and the uses of language
- are thereby opened up to systematic inquiry.