• its author died before 1954;
• the death date of its author is not known, and it was created before 1904;
• it is an anonymous work, a pseudonymous work, or a work made for hire, and it was created before 1904.

The above provisions are contained in 17 U.S.C. § 303. See also this page for more information.

¹ Some government publications are not subject to copyright, including bills, acts, regulations, court judgments, royal commission and select committee reports, etc. See references [1] or [2] for the full list.
² means the typographical arrangement and layout of a published work. eg. newsprint.

You must also include a United States public domain tag to indicate why this work is in the public domain in the United States. Note that this work might not be in the public domain in countries that do not apply the rule of the shorter term and have copyright terms longer than life of the author plus 50 years. In particular, Mexico is 100 years, Jamaica is 95 years, Colombia is 80 years, Guatemala and Samoa are 75 years, Switzerland and the United States are 70 years, and Venezuela is 60 years.