The 4th Conference took place in Luxembourg on 6-7 May 1991. For the first time, a President-in-office of the Council participated in COSAC. Mr Jacques Poos, Minister for Foreign Affairs and President of the Council, presented a synthesis report on the Common Foreign and Security Policy of the Union (CFSP), which has been discussed in the Intergovernmental Conference on the political Union. After a general exchange of views on the CFSP most of the delegations expressed their concern on the absence of parliamentary control of the CFSP either by the national parliaments or by the European Parliament.
The Conference agreed (in principle) on COSAC’s first Rules of Procedure. The Chairmen of the European Affairs Committees had met on 22 March 1991 in advance of the Conference to prepare a draft. The Rules of Procedure were adopted after difficult discussions. The Conference decided that all decisions should be taken by consensus. In order to enhance the role of the European Parliament in the preparations of future COSAC meetings, it was laid down that the European Parliament would be invited to participate in meetings of the Presidential Troika (composed of the national parliaments of the current, former and future Presidencies).
Only one issue could not be resolved at the Luxembourg conference: the article concerning revision of the Rules of Procedure (point 13 c), because the participating parliaments were split on this issue. The final decision was therefore postponed to the 5th Conference in The Hague. However, consensus was reached on the remaining articles of the Rules of Procedure, and the name COSAC was adopted.