The First Amendment or Amendment One/1 may refer to:

• First Amendment to the United States Constitution, regarding freedom of speech, freedom of the press, religious freedom, freedom of assembly, and right to petition
• Australian Constitution Alteration (Senate Elections) Act, 1906, the first amendment to the Australian constitution
• First Amendment of the Constitution of India, which amended several of the Fundamental Rights in India
• First Amendment of the Constitution of Ireland, passed during World War II, concerning the declaration of a national emergency
• First Amendment to the Constitution of Pakistan, which accounted for the secession of Bangladesh
• First Amendment of the Constitution of South Africa, which made three technical changes

• 2004 Georgia Amendment 1, bans same-sex marriage, civil unions and civil union equivalents
• 2004 Kentucky Amendment 1, bans same-sex marriage, civil unions and civil union equivalents
• 2004 Louisiana Amendment 1, bans same-sex marriage, civil unions and civil union equivalents
• 2004 Mississippi Amendment 1, bans same-sex marriage
• 2005 Kansas Amendment 1, bans same-sex marriage, civil unions and civil union equivalents
• 2006 Tennessee Amendment 1, bans same-sex marriage
• 2012 Minnesota Amendment 1, purposed ban on same-sex marriage
• North Carolina Amendment 1, bans same-sex marriage, civil unions and civil union equivalents
• South Carolina Amendment 1, bans same-sex marriage, civil unions and civil union equivalents