A friend and colleague of mine asked on Facebook if it’s possible in $\LaTeX{}$ to include a citation (or several) in the main text without the reference(s) actually appearing in the bibliography section. For example, in the following text, Smith (2015) and Johnson (2015) are both cited, but Johnson (2015) does not appear in the references section.

According to Smith (2015), bluejays are the best; but according to Johnson (2015), cardinals are better.

References

Smith, Mary. 2015. All About Birds. New York, NY: Bird Cage Press.

Note that the bibentry package allows you to include a whole citation in the main text, e.g. “According to Johnson, Harry (2015) More About Birds …”. But here, we just want “Johnson (2015)”.

BibTeX solution

As far as I’m aware, this is not (natively) possible with BibTeX: the moment you do \cite{<key>} and then run pdflatex + bibtex, the \bibitem associated with <key> gets added to the .bbl auxiliary file, which is ultimately responsible for the bibliography. Any \bibitems in there appear in the bibliography.

The hacky suggestion I originally gave was to write, cite, and compile everything just as one would normally do when writing a LaTeX document. For example, if the file you’re writing is file.tex, then run:

$pdflatex file$ bibtex file
$pdflatex file$ pdflatex file


or, if you’re using a LaTeX front-end/wrapper, then use whatever button/command is available for typesetting, such as “Typeset” in MacTeX (I think), or latexmk file if (like me) you use latexmk.

Once you’re finished writing and are absolutely 100% sure you won’t be adding or removing or otherwise changing any citations, then open file.bbl and delete any of the bibitems that you wish not to appear in the bibliography. After that, simply run pdflatex file one more time, and you’re done.

NB: Don’t rerun bibtex file (hence, don’t “Typeset” or run latexmk or do anything that would itself rerun bibtex), since that would overwrite file.bbl, and you’d be back to where you started.

The advantage to this solution is that you can more or less maintain your normal LaTeX + BibTeX workflow, up to the very end.

The obvious disadvantage is that, after you’ve gone through all the trouble of removing bibitems from file.bbl, you can no longer typeset your document without fear of overwriting file.bbl. You could, of course, save a copy of the precious .bbl file in case you overwrite it, but then if you want to add new citations to your document, you’ll have to merge the new file.bbl with the copy of the older file.bbl. Quite a mess, and certainly not elegant.

Biblatex solution

A better option is to use Biblatex. I won’t expound here on the advantages of Biblatex over BibTeX, or even on the basics of how to use Biblatex. (Maybe some other time.) See here for a discussion of BibTeX vs. Biblatex, and see here for a crash course in Biblatex.

Among its many features, Biblatex allows you to define bibliographic categories with \DeclareBibliographyCategory{<category>} and then assign categories to your bibliographic entries with \addtocategory{<category>}{<key>}. The categories can be anything at all. Once you’ve assigned categories to your entries, you can use commands that are sensitive to those categories. One such command is the \printbibliography command, which replaces LaTeX’s normal \bibliography{...} command at the end of the document.

Normally, \printbibliography does just that: it prints the bibliography. But you can give it some options, such as \printbibliography[category=<blah>], which prints a bibliography containing all and only entries of the category blah. Or you can do \printbibliography[notcategory=<blah>], which prints a bibliography containing all and only entries that are not of the category blah.

So the solution is to create a new category for the entries that we want to cite in the main text but suppress in the bibliography. We do that by issuing \DeclareBibliographyCategory{ignore} (the category name can be anything) in the preamble, and then tagging the entries we want to ignore by issuing \addtocategory{ignore}{<key>}.

Here is a minimal working example:

\documentclass{article}
\usepackage[style=authoryear]{biblatex}
\DeclareBibliographyCategory{ignore}

\begin{document}

\cite{johnson2015},
\cite{smith2015},
\cite{doe1986},
\cite{samson2012}

\printbibliography[notcategory=ignore]
\end{document}


With this code, all four references will get cited in the main text, but Johnson (2015) and Doe (1986) will not appear in the bibliography section.

Moreover, the solution is exetnsible: if you decide later that you want to omit Smith (2015) from the bibliography, simply add \addtocategory{ignore}{smith2015} to your preamble. if you decide that you do want Johnson (2015) in the bibliography, simply delete or comment out the line \addtocategory{johnson2015}.
The only disadvantage that I can see is that you need to use Biblatex. Of course, users of Biblatex would hardly see this as a disadvantage. But there are certainly at least some minor disadvantages to using Biblatex, especially if you’ve never used it before. One is that you have to learn what commands to include before and after the document, as well as some new \cite commands. But that’s easy. A more serious potential problem is that you simply cannot use Biblatex. For example, you’re submitting to a journal that doesn’t allow it, or you’re collaborating with someone who refuses to use/learn it. Hopefully, though, in due time, Biblatex will come to supersede BibTeX + natbib, and these will be non-issues.
NB: The solution presented here is based on a comment by Daniel Gutzmann, who suggested creating several bibliographies based on keywords, and then printing only those bibliographies containing (or lacking) a specific keyword. The advantage of my solution is that you can still use a single master .bib file and then categorize the entries in the preamble. If you wanted to reproduce the effect across several documents, you could hardcode the categories onto the entries in the actual .bib file by adding \DeclareBibliographyCategory{<category>} and \addtocategory{<key>} to the @preamble of your .bib file.