One of the EU’s strategies for tackling challenges related to EU membership, and per se a pre-condition for accession, is regional cooperation and good neighbourly relations. Interdependence and de facto cooperation between neighbouring countries in one area (such as infrastructure, transport, energy, free trade) is expected to lead to further cooperation in a broader range of areas, but also to regional stability, reconciliation and ultimately to European integration. Lessons can be drawn from examples of cooperation between the Visegrad and the Baltic countries, but for the Western Balkans, in view of their ethnic disputes and past armed conflicts, building close regional ties and trust is even more crucial. Although not all countries from the region have opened accession negotiations, they are all involved in the Stabilisation and Association Process (SAP), the framework aiming to prepare them for eventual membership. The SAP places particular emphasis on regional cooperation and good neighbourly relations. Regional cooperation has advanced and ‘taken root’ in the Balkans for multiple reasons and has been ‘a transformative experience’. Apart from economic arguments (faster economic growth in general and smoother integration in the EU), there have been political reasons for strengthening regional cooperation. The need to establish permanent conditions for security, stability, peace and development has been a major driver. Since the 1990s, multiple formats and initiatives for regional cooperation covering a wide range of areas have been established in the Western Balkans. Starting with the 1999 Stability Pact for south-eastern Europe, the Western Balkan states have come together in a variety of formats and initiatives with a wide scope, including economic, functional, political and security cooperation.