http://travel.state.gov have information about obtaining a visa for
those traveling to the United States. Both sites have links to websites for
U.S. embassies and consulates worldwide. The embassy and consulate websites
have very helpful information about procedures, timelines, communities
served, required documentation, and fees.
International registrants should be particularly aware and careful about
visa requirements, and should plan travel well in advance. All visa
inquiries must be handled by ACM HQ. Please send your request for a letter
in support of a visa application to
email@example.com include your name, mailing address,
and fax number, as well as the name of the conference you are attending.
(Authors of papers/posters should also include the title). Please note that
ACM does not issue formal “letters of invitation” to any of its conferences.