The International Amateur Radio Union (IARU) is a federation of national associations of certified radio amateurs, representing over 160 countries and separate territories around the world. These Member Societies are elected to IARU membership through a vote of existing member societies.
There can be only one Member Society in each country or separate territory. Member Societies have certain obligations to IARU to:
1) Adequately represent the interests of amateurs throughout the country and/or separate territory, which it proposes to represent
2) Meet its financial obligations as a member of the IARU
3) Be in a position to legally act in the furtherance of IARU objectives within its country and/or separate territory
4) Always act in the interests of amateur radio and IARU and
5) Adhere to the Constitutions of both the IARU and the respective regional organization.
Organisations considering joining IARU should download the application form for IARU membership and follow the guidelines therein.
A list of current member societies and key contacts can be found here