Notwithstanding the functional and technocratic basis of the European integration process, and the fact that the accession criteria hardly mention security issues, the 2004 eastern enlargement brought to the forefront of EU politics important geopolitical and security issues. Eastern enlargement came on to the agenda of the EU in the wake of 1989s peaceful revolutions in Central and Eastern Europe. Security and geopolitics mattered to the decision taken by the EU to embark on expansion in the early 1990s, and thereafter security issues remained prominent in enlargement debates. This article seeks to analyse the most important geopolitical issues which eastern enlargement brought to the fore. In exploring the geopolitical dimension of the eastern enlargement process the article foregrounds some key issues including: the potential power realignments in Europe triggered by enlargement, the EU relationship with Russia and its importance to the unfolding of the enlargement process, and how eastern enlargement was conceived as a mechanism for stabilising the EU’s external environment. The article contrasts realist and constructivist images of post 1989 Europe and the eastern enlargement process and assess their contribution to enlargement scholarship. It argues that constructivist imagery best explains the way in which EU actors interpreted key geopolitical issues within the enlargement framework. In particular it presents enlargement as the expansion of the existing European security community where geopolitical issues were subject to a process of securitisation and desecuritisation.