In legal citations, id. tells the reader you’re citing the exact same source you just cited, and id. at followed by a page number tells them you’re citing that same source but pointing to a different page. Both are italicized, both require that the citation immediately before them refers to a single authority, and both come from the Latin idem, meaning “the same.”
When Each Form Applies
The choice between the two comes down to whether the page number has changed.
Use id. alone when the source and the pinpoint page are identical to the citation directly above. If your first footnote cites Johnson v. Phelan, 69 F.3d 144, 145 (7th Cir. 1995), and your second footnote references the same passage, footnote 2 reads simply Id.
Use id. at [page] when you’re staying with the same source but sending the reader somewhere else in it. If footnote 1 cites Johnson at 145 and footnote 2 discusses something the court said at 150, footnote 2 reads Id. at 150.
Both versions work only when the citation immediately preceding refers to one source. If the previous footnote or citation sentence listed two or more authorities, id. is unavailable under Bluebook rules because the reader cannot tell which source you mean.
Formatting Rules That Get Missed
Bluebook Rule 4.1 lays out the requirements, and editors notice when writers slip.
- Italicize id., including the period. Underlining is accepted in some court filings, but italics are the default.
- Keep the period. Because id. is an abbreviation of idem, the period is part of the form. Dropping it is an error.
- Capitalize the “I” when Id. starts a citation sentence or opens a footnote. When it appears as a citation clause embedded inside a sentence, it stays lowercase.
- Do not italicize “at.” Only id. takes italics; the word “at” and the page number that follow are in regular type.
A correctly formatted pinpoint looks like this: Id. at 237.
When You Cannot Use “Id.”
Several situations block the shorthand, and misusing it in these contexts creates real confusion about which source supports the point.
An Intervening Citation Broke the Chain
If any other authority appears between your current citation and the source you want to reference, id. is off the table. The shorthand refers only to the immediately preceding source. Once another case, statute, or article interrupts, you need a different short form or the full citation. One exception: sources that appear only inside an explanatory parenthetical, or as part of a case’s prior history, do not count as intervening authorities, so id. remains available.
The Previous Citation Listed Multiple Authorities
When the preceding citation is a string cite with two or more sources separated by semicolons, id. creates ambiguity under the Bluebook and cannot be used. Fall back on the case’s short-form name or another appropriate short citation.
Internal Cross-References
Navigation tools like “see supra note 12” or “see infra Part III” are not citations to external authorities. The Bluebook treats them separately under Rule 3.5, and id. has no role there.
Same Source, Same Page
When the pinpoint has not changed, do not add “at” and repeat the page number. Write Id. by itself. Adding “at” with the same page number is redundant, and most editors will flag it.
Statutes and Regulations
When your previous citation was a statute rather than a case, id. still works, but the format shifts. Instead of “id. at [page],” use id. followed by the section symbol and the new section number. The word “at” drops out because statutes are organized by sections, not pages. If you previously cited 42 U.S.C. § 1983 and now want § 1985 of the same title, the citation reads Id. § 1985. The same logic applies to regulations organized by paragraph or subsection.
How “Id.” Differs From “Supra”
Id. refers only to the citation immediately above. Supra reaches back further, pointing the reader to a source cited in an earlier footnote that is no longer the most recent one. If three footnotes have passed since you last cited an article, id. will not work, but supra with the original footnote number will.
Supra carries its own limits. Under Bluebook Rule 4.2(a), it is available for books, articles, reports, and similar secondary materials. It is not available for cases, statutes, constitutions, or regulations. For those sources, if id. is blocked by an intervening citation, use the source-specific short form: an abbreviated case name with a pinpoint for cases, or a shortened code citation for statutes.
Bluebook and ALWD Diverge on One Point
Most law schools teach the Bluebook, but the ALWD Guide to Legal Citation is also widely used, and its rule on id. after a string cite differs. Under the Bluebook, id. is forbidden when the immediately preceding citation contains multiple authorities. Under ALWD Rule 11.2, id. is permitted after a string cite as long as you’re referring to the last authority listed. A citation that violates Bluebook rules may be correct under ALWD. Confirm which manual your court, journal, or professor requires before you write.
Check the Local Court Rules
The Bluebook and ALWD set the baseline, but individual courts can override them. Many federal and state courts maintain local citation rules that modify or replace standard conventions, including specific formats for state reporters and preferences on short-form usage. A citation that is perfect under the Bluebook can still draw a correction if the court’s standing order says otherwise. Read the local rules for the specific court before filing.