How to escape the & (ampersand) character in BibTeX?

I have no problem with

publisher = {Harold \& Maude},

and running again bibtex and pdflatex

When you've typed correctly in the .bib file but still receive errors, go check your .bbl file.

What I usually do is

1. Delete the whole erroneous line in the .bbl file, save, then close the file.
2. Make corrections or dummy (temporary) changes in the .bib file, then compile.

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This is an example from my .bbl file:

\bibitem{Mohanty2005}

A.~K. Mohanty, M.~Misra, and L.~T.
Drzal.

\newblock {\em {Natural Fibers,
Biopolymers, and Biocomposites}}.

\newblock Taylor {\&} `&` Francis Group,
Florida, 2005.

\newblock ISBN-10: 0-8493-1741-X.

The & is the culprit, not {\&}.

What i do is delete the whole line (newblock Taylor {\&} & Francis Group, Florida, 2005.), save, then close the .bbl file. Make corrections or dummy changes in the .bib file, then compile.

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You can simply delete the & in the .bbl file but the next time you make a change in the field that contains that & and compile your .bib file, the error will return.

Clear your auxiliary files and then use the \& escape.

EDIT - and by auxiliary files, I mean that many GUI-based editors have a button or menu option for doing this. If you are doing it manually, delete the .bbl file (and perhaps the .aux file) and this should help.