Diplomats and other foreign government officials traveling to the United States to engage solely in official duties or activities on behalf of their national government must obtain A-1 or A-2 visas prior to entering the United States. They cannot travel using visitor visas or under the Visa Waiver Program. With the exception of a Head of State or Government — who qualifies for an A visa regardless of the purpose of travel — your position within your country’s government and your purpose of travel determine whether you need an A-1 or A-2 visa. Immediate family members of diplomats and government officials receive A-1 or A-2 visas, with few exceptions. Personal employees, attendants, or domestic workers for diplomats and government officials (holding a valid A-1 or A-2 visa) may be issued A-3 visas.
To qualify for an A-1 or A-2 visa, you must be traveling to the United States on behalf of your national government to engage solely in official activities for that government. The specific duties or services that will be performed must be governmental in character or nature, as determined by the U.S. Department of State, in accordance with U.S. immigration laws. Government officials traveling to the United States to perform non-governmental functions of a commercial nature, or traveling as tourists, require the appropriate visas and do not qualify for A visas. The fact that there may be government interest or control in a given organization is not in itself the defining factor in determining if you qualify for an A visa.
Find out How to Apply at travel.state.gov.