Out of the 27 EU member states, 21 are also members of NATO. Another four NATO members are EU applicants—Albania, Montenegro, North Macedonia and Turkey. Two others—Iceland and Norway—have opted to remain outside of the EU, however participate in the EU's single market. The memberships of the EU and NATO are distinct, and some EU member states are traditionally neutral on defence issues. Several EU member states were formerly members of the Warsaw Pact. Denmark has an opt-out from the CSDP.
The Berlin Plus agreement is the short title of a comprehensive package of agreements made between NATO and the EU on 16 December 2002. These agreements were based on conclusions of NATO's 1999 Washington summit, sometimes referred to as the CJTF mechanism, and allowed the EU to draw on some of NATO's military assets in its own peacekeeping operations.