Peacekeeping is not mentioned in the Charter as a tool for the United Nations to employ in the control of conflicts. It was developed during the initial years of the UN as a method to contain armed conflicts in areas where warring parties were in need of a neutral party to observe the peace process. 

The concept of peacekeeping is based on ad hoc practice, and belongs in  the "gray zone" between Chapters VI and VII of the Charter: 

• Chapter VI describes the means of pacific settlement of disputes by negotiation, enquiry, mediation, conciliation, arbitration, judicial settlement, resort to regional agencies or arrangements, or other peaceful means 
• Chapter VII refers to the Security Council's power to authorize economic, diplomatic, and military sanctions, as well as the use of military force, to resolve disputes

Peacekeeping operations are established by the Security Council which holds the primary responsibility under the Charter for international peace and security and provides the political mandate for the operations, the General Assembly provides the budget, while the operational control belongs to the Secretary-General and his Secretariat.  

There has been a dramatic increase in the number of peacekeeping operations after the Cold War, accompanied by a change in their nature. To ensure sustainability they have come to involve more and more non-military elements.