The green card is formally known as the Alien Registration Receipt Card, Form I-151 or I-551. The first receipt cards were Form AR-3 (printed on white paper), and were the product of the Alien Registration Act of 1940. Designed as a national defense measure, the Act required all aliens (non-U. S. citizens) within the United States to register with the U.S. Government. They registered at Post Offices, and their registration forms were forwarded to the Immigration and Naturalization Service (INS) for processing. After processing, a receipt card (Form AR-3) was mailed to each registrant as proof of their compliance with the law. The Alien Registration Act, however, did not discriminate between legal and illegal alien residents. All were registered, and all received AR-3's in return.

As World War II ended and large-scale immigration to the United States resumed, alien registration ceased to take place at Post Offices and became part of regular immigration procedure. Aliens registered upon entry at the port, and the INS issued different documents to different aliens to serve as their Alien Registration Receipt Cards. Which document an alien received depended on his or her admission status. For example, visitors received an I-94c, temporary foreign laborers received an I-100a, and permanent residents received the I-151. This method not only reduced the number of forms handled by the INS, but helped to identify the immigration status of each alien. Thus the small, green, I-151 had immediate value in identifying its holder as a LPR, entitled to live and work indefinitely in the United States. As early as 1947, LPR's protested delays in processing their I-151's, complaining that employers would not hire them until they could prove their permanent resident status.

Following passage of the Internal Security Act of 1950, new regulations issued by the INS rendered Alien Registration Receipt Card Form I-151 even more valuable. As noted above, the AR-3 Alien Registration Receipt Card (issued primarily in the early 1940's) bore no relation to an alien's legal or illegal status. Effective April 17, 1951, regulations allowed those holding AR-3 cards to have them replaced with a new Form I-151 (the green card). Just as I-151 were only issued to Lawful Permanent Residents entering through ports, only aliens with legal status could have their AR-3 replaced with an I-151. Aliens who applied for replacement cards but could not prove their legal admission into the United States, and for whom the INS had no record of legal admission, did not qualify for LPR status and might even be subject to prosecution for violation of U.S. immigration laws.

United States Permanent Resident Card (Green Card)

A United States Permanent Resident Card, also known popularly as Green Card, is an identification card for a permanent resident of the United States of America who does not have U.S. citizenship. It is proof that the holder has permission to permanently reside and take employment in the U.S. Its former official title was Alien Registration Receipt Card, and it is now officially called a Permanent Resident Card, also referred to as form I-551.

The name "green card" comes from the fact that the cards were originally green. Their color has changed over the years, but the term "green card" has remained in use. As of 2005, the card is mostly white and the only prominent green feature is the lettering on the back of the card. A card includes the holder's name and photograph, and other information, and has been updated over the years with numerous anti-counterfeiting devices.

The card must be in the possession of the U.S. permanent resident at all times. This means the U.S. permanent resident must have a currently valid card on their person at all times, to show to an USCIS (U.S. Citizenship and Immigration Services) officer, if requested. One interesting aspect of American law is that permanent residents are required to carry identification cards, but citizens are not. This is simply a consequence of the fact that citizens are, of course, entitled to more constitutional rights than permanent residents, who are still classified as aliens. Before Sep 11, 2001, except when the permanent resident is returning from foreign travel, in reality the requirement to carry the green card was practically never enforced when the resident was simply residing or traveling domestically. After Sep 11, 2001 it does happen that an official from the US Department of Homeland Security randomly asks people if they are US citizens or not and in the latter case then require seeing the Permanent Resident Card or other proof of legal status.

Green cards were formerly issued by the INS (Immigration and Naturalization Service). That agency has been absorbed into and replaced by the new U.S. Citizenship and Immigration Services (USCIS), formerly the BCIS (Bureau of Citizenship and Immigration Services) in the Department of Homeland Security.

It is possible that an alien wants to work while the application for a green card is pending. EAD (Employment Authorization Document) is needed in this case.

Something about Identity Card

Identity document
An identity document is a piece of documentation designed to prove the identity of the person carrying it. Unlike other forms of documentation, which only have a single purpose such as authorizing bank transfers or proving membership of a library, an identity document simply asserts the bearer's identity. If an identity document is in the form of a small standard-sized card, such as an ISO 7810 card, it is called an identity card.

Identity cards can be controversial, as depending on the way they are used by government. If the circumstances where they must be produced covers everyday life and if enough information about use is stored on databases, this can make government surveillance of citizens much easier.

Types of identity cards
Modern identity cards bear little resemblance to the original "photograph on piece of cardboard" and are often hi-tech smartcards which can be read by computer.

Where the identity card is issued by a state, it asserts a unique single civil identity for a person, thus defining that person's identity purely in relation to the state. New technologies allow identity cards to contain biometric information, such as photographs, face, hand or iris measurements, or fingerprints.
Other information typically present on the cards — or on the supporting database — includes full name, parents' names, address, profession, nationality in multinational states, and blood type.

Legal impact
Laws usually limit who is authorized to require an identification (for example limiting it to police, immigration officers etc), though practice usually broadens the range to many public and private entities: for example, a shopkeeper or cashier may request an ID document to be shown by a client paying with a credit card or cheque. Similarly, in circumstances where law enforcement can legally ask for identification, not being able to show an ID document, though legal, may result in being taken to a police station for further identification, depending on the jurisdictions. This can lead to functionality creep whereby carrying a card becomes de facto if not de jure compulsory.

In many cases, other forms of documentation such as a driver's license, passport, or Medicare card serve a similar function, identifying the bearer in a variety of contexts. However, possession of these documents is typically optional from a legal point of view.

Not carrying a required identity card can be beneficial for people who wish to avoid detection, such as innocent citizens who value their privacy. It may also help in some illegal dealings; for instance, in certain countries, the procedures for deporting illegal immigrants whose age, identity or nationality cannot be formally established are more complex than those for whom they can be readily asserted, giving the illegal immigrant more time to prepare his or her defense.