There are currently 193 UN Member States. Each of the Member States of the United Nations has one seat in the General Assembly.
Information about current members, growth of membership since 1945, and the procedure of how a country becomes a member is available on the UN website. Documents by and about members can be found in the UN Digital Library and other sources.
UN Charter, Chapter II, Articles 3-6 concern Membership in the UN. Only states can be members of the United Nations.
Membership in different organs of the UN varies.
Membership of the principal organs is determined by the Charter of the United Nations and the Statute of the International Court of Justice:
In accordance with the Charter, the General Assembly (Article 22), Security Council (Article 29) and the Economic and Social Council (Article 68) may establish subsidiary organs. The decision to establish a subsidiary organ (also called the mandate) usually includes:
The Charter of the United Nations / 
Oppenheim's International Law /
The United Nations, whose specialized agencies were the subject of an Appendix to the 1958 edition of Oppenheim's International Law: Peace, has expanded beyond all recognition since its founding in 1945.This volume represents a study that is entirely new, but prepared in the way that has become so familiar over succeeding editions of Oppenheim. An authoritative and comprehensive study of the United Nations' legal practice, this volume covers the formal structures of the UN as it has expanded over the years, and all that this complex organization does. All substantive issues are addressed in separate sections, including among others, the responsibilities of the UN, financing, immunities, human rights, preventing armed conflicts and peacekeeping, and judicial matters. In examining the evolving structures and ever expanding work of the United Nations, this volume follows the long-held tradition of Oppenheim by presenting facts uncoloured by personal opinion, in a succinct text that also offers in the footnotes a wealth of information and ideas to be explored. It is book that, while making all necessary reference to the Charter, the Statute of the International Court of Justice, and other legal instruments, tells of the realities of the legal issues as they arise in the day to day practice of the United Nations. Missions to the UN, Ministries of Foreign Affairs, practitioners of international law, academics, and students will all find this book to be vital in their understanding of the workings of the legal practice of the UN. Research for this publication was made possible by The Balzan Prize, which was awarded to Rosalyn Higgins in 2007 by the International Balzan Foundation.
The Procedure of the UN Security Council / 
United Nations Handbook / Chinese: 联合国会员国
English: UN Membership
French: Les membres de l'Organisation des Nations Unies
Russian: Членство в Организации Объединенных Наций
Spanish: Miembros de la ONU
In the context of the Charter, membership and participation in the UN are different.
UN Charter, Chapter II, Articles 3-6 concern Membership in the UN. Only states can be members of the United Nations.
Membership in different organs of the UN varies.
To research these matters further, consult secondary sources about the organ or the article of the Charter. For example, the Repertoire of the Practice of the Security Council has a section on the Council's role in membership as well as section on participation in the Council.
Current regional groups and their members are listed on the UN Department of General Assembly and Conference Management website:
Chairs of the regional groups rotate monthly and are listed in the General Information section of the Journal of the United Nations.
Excerpts from the UN legal opinion of 4 March 2003 (2003 UN Juridical Yearbook p. 529):
General Assembly resolutions that set out the initial basis for the development of the regional groups include:
Please note that there are also additional types of groups of states for negotiations outside the UN, such as various Groups of Friends, the Non-Aligned Movement (NAM), the Group of 77 (G77), etc. Regional group names may differ from those set out in the resolutions on Council membership.
