Yes. Under the Bluebook, the period after “id.” is italicized in Bluebook citations, right along with the “i” and the “d.” The abbreviation and its period form a single unit, and all of it gets italic formatting every time the citation appears.
Why the Period Belongs in Italics
“Id.” is short for the Latin idem, meaning “the same.” The period isn’t punctuation separating one thing from another. It marks the abbreviation itself, the same way the period in “Dr.” or “etc.” does. Rule 4.1 treats the letters and the period as one word, so the formatting applied to the letters applies to the period too.
A quick test settles most close calls. Spell out the full word idem in place of the abbreviation. If the period disappears when you do that, it was part of the abbreviation and should be italicized. If the period stays because it was ending the sentence, it belongs to the sentence and stays in regular font.
Which Punctuation Stays Roman
Only the period that signals the abbreviation gets italics. Punctuation that belongs to the surrounding sentence does not. A comma after “id.” within a citation clause is roman. A sentence-ending period that follows the abbreviation’s own period is roman. You can end up with two periods back to back, one italic and one not, when “Id.” closes a sentence. That looks odd, but it is correct.
Capitalization and Pinpoint References
Capitalize the “I” only when “Id.” begins a citation sentence. Inside a textual sentence, as a citation clause set off by commas, use lowercase “id.” Either way, the period is italic.
When you need to point the reader to a different page in the same source, add “at” and the new page: Id. at 45. The abbreviation and its period are italicized; “at” and the page number are not. The same pattern works for a section or paragraph pin. If the pinpoint is the same page as the previous citation, “Id.” stands alone with no “at.”
Getting It Right in Word
Most of the errors you see in practice aren’t about the rule. They’re about the software. Double-clicking “id.” in Microsoft Word selects the letters and stops at the period. Hit the italics button and you get an italic “id” followed by a roman period. On screen it’s easy to miss. Anyone trained to look for it will catch it immediately.
Two fixes work reliably. Extend the selection manually to include the period before applying italics, or toggle italics on, type “id.” including the period, and toggle italics off afterward. Some writers set up an autocorrect entry or a short macro that formats the whole abbreviation as a unit. Whichever route you take, give the final draft a proofreading pass just for this. Law review editors, judicial clerks, and hiring attorneys notice the roman period, and it reads as a sign that the writer isn’t fluent in citation conventions.