Kumanovo Agreement

The Military Technical Agreement, also known as the Kumanovo Agreement, signed between the International Security Force (KFOR) and the Governments of the Federal Republic of Yugoslavia and the Republic of Serbia, was an accord concluded on 9 June 1999 in Kumanovo, Macedonia. It resulted in the end of the Kosovo War, and established new basic relations between Yugoslavia and the Kosovo Force, which would act to replace units of the Yugoslav Army, in Kosovo.
Background.
The run-up to the Kumanovo Agreement involved a flurry of negotiations not just between Yugoslavia and Serbia but also NATO and Russia. Despite the initial agreement, for instance, on a withdrawal timetable for the Serbian forces in Kosovo, NATO's Operation Allied Force was still underway, pending the completion of full withdrawal of the Serbian troops.
There are sources that cite the role that Russia played in the immediate resolution of the accord. There was a claim about a meeting between Russian Foreign Minister Igor Ivanov and U.S. Secretary of State Madeleine Albright. An initial agreement between the two parties was reached, which involved a commitment on the part of NATO to cease its airstrikes and a willingness to remove a passage it wanted to include in the Kumanovo Agreement in exchange for Russian support for a forthcoming UN Resolution agreed by the Group of Eight. Without the Russian participation, the UN Security Council Resolution on Kosovo would not have been approved and the NATO airstrikes would have continued.
Provisions of the agreement.
The key provisions of the agreement were designed to enable the following:
The NATO presence was sanctioned by the United Nations Security Council on the strength of Resolution 1244 (1999), which authorized UN Member states and international organizations to maintain an international security presence via the KFOR in Kosovo until an agreement is finally concluded and its terms implemented. The KFOR was authorized to take all actions necessary to ensure compliance with the agreement. 
Status of agreement.
Legal expert Enrico Milano has argued that the Kumanovo Agreement "is dubious under the Vienna Convention on the Law of Treaties (VCLT) and, as a consequence, so too are parts of Resolution 1244 referring, implicitly or explicitly, to paragraph 10 of Annex 2 of the same resolution." One particular argument is that "it is doubtful whether the Kumanovo Agreement can be considered valid according to Article 52 of the VCLT, which states that "a treaty is void if its conclusion has been procured by the threat or use of force in violation of the principles of international law embodied in the Charter of the United Nations". The legal arguments continue that in fact to remedy the legal issues arising what is needed is for Status of Forces Agreement to be entered into with Belgrade.