In legal citations, Id. is a short-form citation that points the reader back to the single authority you just cited, saving you from repeating the full reference. Under Bluebook Rule 4.1, you can use it in any citation sentence or clause so long as the immediately preceding citation refers to one source and only one source.1The Bluebook Online. 4.1 Id. Everything else about using it correctly flows from that single rule.
When Id. Is Allowed
Two conditions have to hold. The citation you’re replacing must point to the authority immediately before it, and that preceding citation must contain only one source. If the last citation listed two authorities, say a case and a statute, the reader can’t tell which one you mean, and you need a fresh full citation instead.1The Bluebook Online. 4.1 Id.
One exception preserves the chain. If the preceding citation technically mentions a second source only inside an explanatory parenthetical, a prior or subsequent history note, or an explanatory phrase, those references count as supplemental rather than independent authorities. The reader still knows which source Id. means, so you can use it.
You can stack consecutive Id. citations without limit. As long as nothing interrupts the chain back to the original single authority, each one still works.
One boundary worth flagging: Id. doesn’t cover internal cross-references. If you’re pointing the reader to another part of your own document rather than to an outside source, Rule 3.5 governs instead.1The Bluebook Online. 4.1 Id.
How to Format It
Three details are non-negotiable. Id. is always italicized, and the italicization runs through the trailing period. The period itself is mandatory because Id. is an abbreviation. And capitalization depends on placement: capitalize the “I” only when Id. begins a citation sentence; keep it lowercase mid-sentence or after an introductory signal.
A few courts still have local rules that call for underlining instead of italics, a holdover from typewriter-era practice. Italics are the modern standard in most jurisdictions, but check local rules before you file.2Legal Information Institute. Basic Legal Citation – Underlining and Italics
Pinpoints: When to Use “at” and When to Skip It
If you’re citing the same page as the preceding citation, Id. stands alone. Same source, same spot, nothing more needed.
If you’re pointing to a different page in the same source, add “at” and the new page number: Id. at 45.
Section and paragraph symbols work differently. When the pinpoint uses § or ¶, drop “at” entirely. The correct form is Id. § 7 or Id. ¶ 12, never Id. at § 7. The same holds when you’re citing a neighboring section of a statute you just cited in full.1The Bluebook Online. 4.1 Id. This is one of the most frequently flagged errors in law review editing.
Using Signals Before Id.
Introductory signals like See, Cf., and But see work fine in front of Id. The signal comes first, italicized, followed by a space and then lowercase “id.” Because the signal opens the citation sentence, it gets the capital letter: See id. at 201, or But see id. § 12(b). No comma separates the signal from “id.”
You can also follow a supra or infra cross-reference with Id. without re-establishing a full citation. Those internal navigational cues don’t break the chain.
When the Chain Breaks
The moment you cite a different authority, the chain snaps. It doesn’t matter whether the intervening citation is a single case or a string cite of five sources. Once a new authority appears, you can’t use Id. for the original anymore. You pick back up with either a full citation or an appropriate short form.
Which short form depends on the type of source. A common mistake is defaulting to supra. Under Bluebook Rule 4.2, supra cannot be used for cases, statutes, constitutions, regulations, restatements, or model codes.3The Bluebook Online. 4.2 Supra and Hereinafter That restriction covers most primary authority.
For cases, use one party name plus the volume, reporter, and pinpoint page (e.g., Baker, 369 U.S. at 195). For statutes, repeat the code section. Supra is reserved mainly for secondary sources like books, periodicals, reports, and legislative hearings.3The Bluebook Online. 4.2 Supra and Hereinafter If even supra would be unwieldy, such as for a source with an unusually long title, you can designate a hereinafter short form in brackets at the end of the first full citation.
Court Documents and Law Review Footnotes
The Bluebook treats the two contexts slightly differently. In court documents and legal memoranda, Id. refers back to the immediately preceding authority in the text. In law review footnotes, Id. is valid when citing the same source within the same footnote, or when the immediately preceding footnote contains only one authority.1The Bluebook Online. 4.1 Id. The footnote-to-footnote version catches editors off guard when a preceding footnote turns out to contain a string cite.
Common Mistakes
- Using Id. after a multi-source citation. If the preceding footnote or sentence cited two or more independent authorities, Id. is off the table. This is the single most common error in student-edited law review footnotes.
- Writing Id. at § instead of Id. §. The word “at” bridges to page numbers only. Section and paragraph symbols replace it.
- Capitalizing “id.” after a signal. When See or Cf. starts the citation, the signal carries the capital. See Id. is wrong; it should be See id.
- Reaching for supra to re-cite a case or statute. After the chain breaks, those source types need their own short forms.3The Bluebook Online. 4.2 Supra and Hereinafter
- Forgetting to italicize the period. The italicization covers both the letters and the period. Leaving the period in roman type is technically wrong, though only meticulous editors tend to catch it.
Getting Id. right comes down to one goal: the reader should never have to guess which source you mean. When in doubt, a full citation is always safe. It’s wordier, but it’s never wrong.