A green card is an immigrant visa indicating that the holder is a permanent resident of the U.S. who can work in the country, travel to and from the U.S., and eventually become a U.S. citizen, according to 'Lectrict Law Library.
A permanent resident can travel to and from the U.S. with his green card and a valid passport. Every trip away should not exceed one year, or the green card will be forfeited and a reentry permit will be required, according to DazLaw.com.
Permanent residents who intend to apply for U.S. citizenship should reside in the U.S. for a minimum of half of the time required to qualify for citizenship. This means either 18 months out of a three-year qualifying period or 30 months out of a five-year period.
