United States permanent residents have an identification card known as the “Green Card.” Other names that the Green Card is known as include: immigrant visa, permanent visa, permanent resident card, permanent resident visa, Form I-151 or Form I-551. In the past the identification card was known as an alien registration receipt, which was previously its formal title. While permanent residents are not United States citizens, they are granted permission to reside and work in the United States on a permanent basis. Permanent residents of the United States legally reside in the country, but are still considered aliens. Unlike United States citizens who are not required to carry identification to prove their citizenship, permanent residents must carry their Green Card with them at all times. This is one of the many constitutional rights that United States citizens are entitled to. Before the September 11 terrorist attacks, the requirement to carry one's Green Card at all times was not strictly enforced when traveling within the United States. The only time the status of the permanent resident was checked was when traveling outside the United States. However, post September 11, the U.S. Department of Homeland Security now requires that permanent residents be able to show their Green Card or other document that will prove their legal status in the country at all times. The government agency responsible for issuing Green Cards is the U.S. Citizenship and Immigration Services (USCIS) which was formerly the Immigration and Naturalization Service (INS).

The first alien registration receipt card was introduced with the Alien Registration Act of 1940 and was white. As a security measure all non-U.S. citizens, even if they were in the country illegally were required to register with the government via their local post office. The applications were then forwarded to the Immigration and Naturalization Service (INS) and each applicant received a receipt card or Form AR-3. The card did not differentiate between a legal and illegal resident in the United States. Basically, the card was given to anyone who registered. Toward the end of the World War II and as migration greatly increased, the registration no longer took place at local post offices but with the federal government's offices of the Immigration and Naturalization Service (INS). The INS began to differentiate aliens into three categories: visitors, permanent residents and temporary foreign workers. Visitors received the I-94c, permanent residents the I-151, and foreigner workers the I-100a. The green I-151 identified individuals as having the permanent right to work and reside legally in the United States. The Internal Security Act of 1950 introduced new regulations and made the I-151 more valuable to its holders. Due to its long title, the alien registration receipt card form I-151, everyone from immigration attorneys to enforcement officers started referring to it as the Green Card. The card became highly desirable among many and represented a status they sought to attain. Counterfeit cards became a serious problem and from the 1940s to 1970s and there were a total of 19 different versions introduced. The card’s color was changed to a pale blue and later a dark blue, but it continued to be referred to as the Green Card.

It was not until 1977 when the INS introduced an alien registration receipt card which could not be easily counterfeited. The new card was machine-readable. Some of the varying colors included pink and pink with blue. Nonetheless, it was still referred to as the Green Card. The current Green Card or permanent residency card is predominantly white with black letters. The Green Card includes a person’s name and photograph as well as other information. It is the size of a credit card and is plastic. When looking at the back of the current permanent residency card, the green is more prominent. Throughout the years, it continues to be updated with new anti-counterfeit features. Regardless of the color of the actual card, it will be known as the “Green Card” because the first card that differentiated lawful permanent residents was green and it is a term that has stuck to it. Being a permanent resident in the United States entitles individuals to certain rights and those rights came into existence when the permanent residency card was green. However, there are instances when the Green Card can be revoked. These instances include an individual being outside the United States for an extensive period of time, not maintaining permanent residence in the United States or breaking certain laws.