is a specialized agency of theUnited Nations(UN) that is concerned with international
public health. It was established on 7 April 1948, headquartered inGeneva, Switzerland. The WHO is a member of theUnited Nations Development Group. Its predecessor, theHealth Organization, was an agency of theLeague of Nations. The constitution of the World Health Organization had been signed by 61 countries on 22 July 1946, with the first meeting of the World Health Assembly finishing on 24 July 1948. It incorporated the Office International d'Hygiène Publiqueand the League of Nations Health Organization. Since its creation, it has played a leading role in the eradication of smallpox.