The Universal Postal Union / Union Postale Universelle (the UPU)
     

The Universal Postal Union is an international organization that controls the world's postal system by coordinating postal policies among its member nations.  Each country that's a member of the Universal Postal Union agrees to the same rules for international postal carriage, thereby standardizing postal arrangements.  But before the UPU was established each country had to enter into a separate treaty with each other country in order to regulate international mail to and from that country.

Recognizing that this situation resulted in a hodge-podge of postal rates and confusion, many countries signed the Treaty of Berne to create the "General Postal Union" in 1874.  It quickly revolutionized the processing and delivery of mail throughout the world.  Re-named the Universal Postal Union in 1878, the UPU is now a United Nations agency with its headquarters in Berne, Switzerland.

The UPU ensures that stamps of its member nations are accepted for the entire international route that a piece of mail takes, instead of the previous arrangement where mailers had to affix stamps of every country through which a piece of mail would pass.  It also established a more or less uniform rate to mail a letter anywhere in the world.

The UPU and its uniform policies for mail handling were a great success.  After the United Nations was founded, the Universal Postal Union became one of its agencies.  Any country that's a member of the UN may become a member of the UPU, and other than Andorra, the Marshall Islands, Micronesia and Palau, all 192 United Nations member countries are also UPU members.  Vatican City, although not a member of the UN, is also a member of the UPU.

Throughout the years many countries have issued stamps in honor of the UPU, and many of these stamps feature beautiful designs.  Some stamp collectors form topical stamps collections that consist only of these UPU stamps.  They're generally not expensive to collect, so why not try it?