Citing a website in Chicago depends on which of the two Chicago systems your course uses, and the two produce visibly different papers. This page covers the notes-bibliography form that history and humanities courses expect, with the note and the bibliography entry side by side, since they are punctuated differently.
Chicago wants the same information in a note and in a bibliography entry, but arranged and punctuated differently. The note is a sentence; the bibliography entry is a list of full stops.
In notes-bibliography Chicago there is no in-text citation in the APA sense. A superscript number in your sentence points to a footnote at the bottom of the page, and the note carries the detail.
In your sentence: Air quality has been linked to cardiovascular risk.¹
First note: 1. “Air Quality and Health,” World Health Organization, last modified March 11, 2024, https://www.who.int/example.
Later note: 2. “Air Quality and Health.”
Author-date variant instead: (World Health Organization 2024)
Footnote (first, full)
1. “Air Quality and Health,” World Health Organization, last modified March 11, 2024, https://www.who.int/example.
Footnote (shortened)
2. “Air Quality and Health.”
Bibliography entry
World Health Organization. “Air Quality and Health.” Last modified March 11, 2024. https://www.who.int/example.
Chicago's flexibility is deliberate, because it was written for material that does not fit neat categories. These cases come up often in history coursework.
| The page has no author at all | Begin the note with the page title and let the site name follow it. |
|---|---|
| The site name and the author are identical | Omit the author and start with the title, since repeating it adds nothing. |
| A digitised archival document | Cite the original item, then the collection, then the repository, and add the URL last. |
| A blog post | Treat the blog as the equivalent of a periodical, with the post title in quotation marks. |
| Your instructor wants author-date instead | The same information becomes (World Health Organization 2024) in the text with a References entry. |
| The page carries no date of any kind | This is the case where an access date belongs, and Chicago accepts it as a last resort. |
Chicago asks for a last-modified date when the site provides one, and falls back to an access date only when it does not. This ordering is the opposite of what most students assume, and the reasoning is worth understanding because it applies well beyond Chicago.
An access date records when you looked. A modification date records when the content last changed. Only the second tells a reader whether the version they are seeing is the version you read. If a page says last modified March 2024 and you accessed it in August, a reader arriving in December can check whether the modification date has moved, and know immediately whether the content is the same.
Chicago was designed for historians, and this shows in how it treats sources that shift over time. The same instinct produces its unusually detailed rules for archival material, where the specific item, the collection and the repository each get named. In both cases the goal is that a later reader can retrace exactly what you saw.
History, literature and art history use notes-bibliography, which is what this page shows. The sciences and most social sciences use author-date, where the same page becomes (World Health Organization 2024) in the text.
Only as a fallback. If the page shows a publication or last-modified date, use that. If it shows neither, add an access date so the reader knows which version you saw.
Use the page title in quotation marks alone, or the author and a short title if you cite several pages from the same site. Ibid. was discouraged in the seventeenth edition.
Normally yes, though some instructors accept notes only for web material. Where a bibliography entry is required, remember it inverts the author and uses full stops rather than commas.
The page title in quotation marks alone is usually enough. Add the author before it if you cite several pages from the same site and the titles alone would be ambiguous.
The 18th edition appeared in 2024, but most departments still specify the 17th. Web citation changed very little between them, so either will produce an acceptable reference.
In a note, list up to three in normal order with and before the last. In a bibliography entry, invert only the first. For four or more, give the first followed by et al. in the note and list them all in the bibliography.
Both. The note gives it after the date, and the bibliography entry gives it at the end. Chicago repeats it because notes and bibliography entries are each meant to stand alone.