These are not all the categories established by the Immigration & Naturalization Service, but those below are the most common categories encountered in colleges & universities.
B -- A visitor for business (B-1) or pleasure (B-2)
F -- A non immigrant student pursuing a "full course of study" toward a specific educational or professional objective
H -- Temporary employment or training of foreign nationals by a specific employer.
J -- Exchange Visitor Program, whose purpose is "to increase mutual understanding between the people of the United States and the people of other countries by means of educational and cultural exchanges."
M -- A non immigrant student at a vocational or other nonacademic institution.
O -- for employment of individual aliens who have achieved national or international acclaim for extraordinary ability in the sciences, arts, education, business, athletics, or television and movie industries.
Capstone EMC is authorized to issue the I-20 A-B form leading to the F-1 Student visa.
Other INS categories include:
TN (Trade NAFTA, for Canadian & Mexican business purposes),
A (foreign government employees),
E (foreign traders or investors),
G (representatives of international organizations),
I (foreign media representatives),
K (fiance(e) or a U.S. citizen),
L (intra company transferee),
P (performing artist or athlete),
Q (international cultural exchange),
R (religious workers),
EWI (entry without inspection -- illegal entry),
TPS (temporary protected status -- permits foreign nationals to remain in the U.S. until conditions in their home countries (wars, natural disasters) improve).