The E-2 visa is known as an investor visa or treaty investor visa. It is available only to non-immigrants who are residents of a country that the United States has a treaty of business, commerce and navigation with.
The E-2 visa was created to enhance international commerce and build economic relationships between the United States of America and other countries. It is not designed to be used as a residential visa or as a step in attaining a green card.
E-2 visas are temporary, and the holder is only allowed to enter the United States on it to oversee their enterprise. The maximum length an individual can have an E-2 visa is five years.