The 25 member states participating in PESCO are Austria, Belgium, Bulgaria, the Czech Republic, Croatia, Cyprus, Estonia, Finland, France, Germany, Greece, Hungary, Italy, Ireland, Latvia, Lithuania, Luxembourg, the Netherlands, Poland, Portugal, Romania, Slovenia, Slovakia, Spain and Sweden, according to a Council press release.

Denmark, Malta and the U.K. opted not to join PESCO.

On Nov. 13, ministers from 23 member states signed a joint notification on PESCO and submitted it to the High Representative and the Council; on Dec. 7, Ireland and Portugal also notified of their decision to join.

According to the Council, Permanent Structured Cooperation in the area of security and defense policy was introduced by the Lisbon Treaty, and foresees the possibility of EU member states working more closely together in the area of security and defense. The new permanent framework for defense cooperation will allow willing and able member states to jointly develop defense capabilities, invest in shared projects and enhance the operational readiness and contributions of their respective armed forces.

The Council decision establishing PESCO outlines the list of participating member states; the list of ambitious and more binding common commitments undertaken by participating member states, including "regularly increasing defense budgets in real terms in order to reach agreed objectives"; PESCO governance, with an overarching level maintaining PESCO coherence and ambition, complemented by specific governance procedures at project level; and administrative arrangements, including the secretariat functions for PESCO at project level and financing.

Participating member states also simultaneously adopted a declaration welcoming a political agreement identifying an initial list of 17 projects to be undertaken under PESCO. The projects cover areas such as training, capability development and operational readiness in the field of defense. These initial projects are expected to be formally adopted by the Council early next year.