The name "John Doe" is used as a placeholder name for a male party in a legal action, case or discussion whose true identity is unknown or must be withheld for legal reasons. The name is also used to refer to a male corpse or hospital patient whose identity is unknown. This practice is widely used in the United States and Canada, but is rare in other English-speaking countries (including the United Kingdom itself, from where it probably originates – see "Origin" below). In the United States, the term John Doe is sometimes used to refer to a generic male. On various forms, the first name listed is often John Doe, along with a fictional address or other fictional information, to provide an example of how to fill out the form.

The female equivalent is Jane Doe, whilst a child or baby whose identity is unknown may be referred to as Baby Doe. A notorious murder case in Kansas City, Missouri referred to the baby victim as Precious Doe. Additional persons may be called James Doe, Judy Doe, etc. However, to avoid possible confusion, if two anonymous or unknown parties are cited in a specific case or action, the surnames Doe and Roe may be used simultaneously – for example, "John Doe v. Jane Roe". Other variations are John Stiles and Richard Miles, now rarely used, and Mary Major, which has been used in some American federal cases.

The Doe names are often, though not always, used for anonymous or unknown defendants (but see "origin" below). Another set of names often used for anonymous parties, particularly plaintiffs, are Richard Roe for males and Jane Roe for females (as in the landmark U.S. Supreme Court abortion decision Roe v. Wade).