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Green Cards from WikiPedia:

A United States Permanent Resident Card, also known as a green card (due to its color in the earlier versions), is an identification card attesting to the permanent resident status of an alien in the United States of America. Green card also refers to an immigration process of becoming a permanent resident. The green card serves as proof that its holder, a Lawful Permanent Resident (LPR), has been officially granted immigration benefits, which include permission to reside and take employment in the USA. The holder must maintain permanent resident status, and can be removed from the US if certain conditions of this status are not met.

Green cards were formerly issued by the Immigration and Naturalization Service (INS). During a re-organization process, that agency was absorbed into and replaced by the Bureau of Citizenship and Immigration Services (BCIS), part of the Department of Homeland Security (DHS). Shortly after that re-organization, BCIS was renamed to U.S. Citizenship and Immigration Services (USCIS), which still retains the responsibility for issuing green cards.

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