In legal writing, an id. citation is shorthand for “the same source I just cited.” It comes from the Latin idem, and writers use it so they don’t have to repeat a full case name, statute, or article every time they reference the same authority in consecutive sentences. When you see it in a brief or law review piece, look at the citation directly above it: that is what “Id.” points to.
What Id. Refers To
“Id.” tells the reader that the source is identical to the one in the immediately preceding citation. Rather than writing Miranda v. Arizona, 384 U.S. 436 (1966) a second time, the writer puts “Id.” and the reader knows the same case is still in play. It works for any authority: cases, statutes, regulations, books, and law review articles.
When You Can Use It
Two conditions have to be true at the same time:
- The preceding citation must point to a single authority. If the citation above groups two sources together (say, a case and a statute), “Id.” is ambiguous and can’t be used.
- Nothing can interrupt the chain. If any other source appears between the original citation and your “Id.,” the chain is broken and you need a short-form citation instead.
These rules come from Bluebook Rule 4.1.1The Bluebook Online. 4.1 Id.
Formatting and Punctuation
- Italicize both the letters and the period: Id. The period is part of the abbreviation, not sentence punctuation, so it stays even mid-sentence.
- Capitalize “Id.” when it begins a citation sentence. Use lowercase id. when it follows a semicolon inside a larger citation clause.
Pointing to a Different Page or Section
When you’re citing the same source but a different location inside it, add a pinpoint reference after “at”:
- Different page in a reporter: Id. at 52.
- Westlaw or Lexis screen page: Id. at *3. The asterisk signals an electronic database page rather than a printed reporter page.
One exception trips people up. When the pinpoint uses a section symbol (§) or paragraph symbol (¶), drop the word “at.” Write Id. § 12, not Id. at § 12.1The Bluebook Online. 4.1 Id.
If you’re citing the exact same page as the preceding citation, “Id.” stands alone with nothing added after it.
Examples
A basic repeat to the same source and same page:
The Court held that custodial interrogation requires a Miranda warning. Miranda v. Arizona, 384 U.S. 436, 479 (1966).
This requirement applies regardless of the severity of the offense. Id.
Same source, different page:
Miranda v. Arizona, 384 U.S. 436, 479 (1966).
Id. at 467.
A broken chain:
Miranda v. Arizona, 384 U.S. 436, 479 (1966).
See also Terry v. Ohio, 392 U.S. 1, 19 (1968).
Id. ← now refers to Terry, not Miranda.
Once Terry appears, “Id.” attaches to it. To return to Miranda, you’d need a short-form citation such as Miranda, 384 U.S. at 479.
Id. in Footnotes
Law review articles and some court filings place citations in footnotes, and the rule shifts slightly there. You can use “Id.” to refer to the immediately preceding authority within the same footnote, or to the sole authority in the immediately preceding footnote.1The Bluebook Online. 4.1 Id.
The single-authority requirement still holds. If footnote 5 cites three sources, footnote 6 can’t open with “Id.” because the reference would be unclear.
Authorities that appear only in parentheticals, explanatory phrases, or prior history within a footnote are generally ignored when deciding whether the footnote contains a single authority. So if footnote 5 cites one primary case and mentions another only in a parenthetical, footnote 6 can still use “Id.” for the primary case.
Common Mistakes
- Using “Id.” after a multi-source citation. If the preceding sentence cited a case and a statute together, “Id.” is ambiguous. This is probably the most frequent error, and citation editors catch it immediately.
- Forgetting that a parenthetical source breaks the chain in body text. In court documents, a source mentioned inside a parenthetical generally counts as an intervening authority. Footnote practice is more forgiving.
- Using “Id.” for internal cross-references. To point the reader to another part of your own document, use “supra” (backward) or “infra” (forward), not “Id.”
- Dropping the period. “Id” is wrong. The period is part of the abbreviation.
When Id. Isn’t Available
Once the chain of immediate succession breaks, you have two alternatives.
A short-form citation repeats enough of the original to identify it. For cases, that typically means the first party name and the reporter page: Miranda, 384 U.S. at 479. For statutes, you repeat the code section. Short forms work for any type of authority and are the standard fallback when “Id.” isn’t available.
“Supra” means “above” and sends the reader back to an earlier footnote for the full citation. It’s used for books, articles, reports, and similar secondary materials. Supra is not available for cases, statutes, constitutions, or most legislative materials; those take short-form citations instead.2Legal Information Institute (LII). 6-500 Short Form Citations