How to cite chapter in book?

Don't use @inbook ever for anything. Use one of the following, depending on the situation:

• @book and \cite[Chapter~5]{foo} for a monograph.

• @incollection for a book in which each chapter has a different author. Then the relevant fields are booktitle= and title=; this is similar to @inproceedings.

I think the best policy is never to talk of chapter numbers in the reflist at all, and move talk of chapter numbers, on the few occasions they are needed, to the citation in the main text. But of course you can't always choose. So, if you must use a particular Bibtex style that uses chapters, then include them in your *.bib files, and avoid Bibtex styles that allow you to refer to chapter numbers in the reference list whenever you can.

Notes on citation style

Citation styles vary, but IMO the cleanest policy is the following:

• Do not refer to chapters in the reference list (i.e., what Bibtex calls the bibliography, but the {thebibliography} environment calls the References section/chapter), and refer only to page numbers in references for articles in journals and collected articles;
• Citations of chapters and page numbers within works cited in the reflist should consist of the identifier of the work cited in the reflist, together with the specification of the part of the work of interest;
• Volume numbers are trickier... I could say more, but for the sake of brevity, I won't.

This policy is followed by The Chicago Manual of Style and the Publication Manual of the APA, and is supported by the {natbib} and {apalike} Bibtex styles.

Example

Reflist

• Boolos, G., 1971/1998. 'The iterative conception of set'. In R.C. Jeffrey (ed.), Logic, Logic, and Logic, Harvard University Press, pp. 13-29. First published, The Journal of Philosophy, 68:215-232.
• Johnstone, P.T., 1987. Notes on Logic and Set Theory. Cambridge University Press.

(We are interested in chapter one of the collected articles of George Boolos, a fact we never mention, since we have the title of the chapter and the page numbers in the reflist. We are interested in three chapters of Peter Johnstone's work, which we don't mention in the reflist, but do in the citation in the main text).

Citations in main text

The cumulative hierarchy had a long prior history, but was not taken seriously as the intellectual foundation of Zermelo-Fränkel set theory until the landmark work of Boolos (1971). In the following, we shall assume the treatment of ZFC given by Johnstone (1987, chapters 5-7).

For the various fields, I usually check the BibTeX article in Wikipedia. I believe you want @inbook to cite a chapter. Normally, I'll just write \cite[Chapter~5]{foo}, though.

From the Wikipedia link, the required fields for @inbook are: author/editor, title, chapter/pages, publisher, year and the optional fields are volume, series, address, edition, month, note, key.