A green card, known officially as a permanent resident card, is an identity document which shows that a person has permanent residency in the United States. Green card holders are formally known as lawful permanent residents (LPRs). As of 2019, there are an estimated 13.9 million green card holders, of whom 9.1 million are eligible to become United States citizens. Approximately 65,000 of them serve in the U.S. Armed Forces.

Green card holders are statutorily entitled to apply for U.S. citizenship after showing by a preponderance of the evidence that they, among other things, have continuously resided in the United States for one to five years and are persons of good moral character. Those who are younger than 18 years old automatically derive U.S. citizenship if they have at least one U.S. citizen parent.

The card is known as a "green card" because of its historical greenish color. It was formerly called a "certificate of alien registration" or an "alien registration receipt card". Absent exceptional circumstances, immigrants who are 18 years of age or older could spend up to 30 days in jail for not carrying their green cards.

Green card applications are decided by the United States Citizenship and Immigration Services (USCIS), but in some cases an immigration judge or a member of the Board of Immigration Appeals (BIA), acting on behalf of the U.S. Attorney General, may grant permanent residency in the course of removal proceedings. Any authorized federal judge may do the same by signing and issuing an injunction. Immigrant workers who would like to obtain a green card can apply using form I-140.

An LPR could become "removable" from the United States after suffering a criminal conviction, especially if it involved a particularly serious crime or an aggravated felony "for which the term of imprisonment was completed within the previous 15 years."