Id.
A short-form citation meaning 'the same source as the one immediately preceding' — the legal cousin of 'ibid.'
'Id.' is an abbreviation of the Latin 'idem', 'the same'. In legal writing under the Bluebook, it is used in footnotes to refer to the source cited in the immediately preceding citation, with or without a new pin cite. 'Id. at 501' means 'the same source as the last footnote, page 501'.
Id. is the workhorse of legal footnotes because litigation-style writing tends to lean on a small number of authorities and refer to them again and again. Instead of repeating the full case name and reporter each time, the writer signals continuity with 'Id.' and updates only the page. The result is footnotes that stay readable even when a paragraph relies on the same source for five straight sentences.
The rule is strict: 'Id.' refers only to the immediately preceding citation. If any other source has been cited in between — even in a parenthetical — the writer must return to the full citation or use an appropriate short form. Misused 'Id.' is one of the fastest ways to lose a reader's trust in a brief.
Common mistake: treating 'Id.' as interchangeable with 'ibid.' Both mean 'the same', but 'ibid.' is standard in humanities citation (Chicago notes-and-bibliography, older MLA) and typically appears with a page number as 'ibid., 12'. 'Id.' belongs to legal style. Mixing them in a single document reads as sloppiness.
“1. Brown v. Board of Education, 347 U.S. 483, 495 (1954). 2. Id. at 494.”
Keep reading the glossary
A citation shorthand meaning 'in the same source as the previous note'.
A citation shorthand meaning 'in the work already cited'.
A citation that points to the exact page, paragraph, or section where a quoted or paraphrased passage appears.
An in-text source reference given in parentheses, keyed to a fuller entry in the bibliography.