Setting bold Greek letters in LaTeX maths

The issue here is complicated by the fact that \mathbf (the command for setting bold text in TeX maths) affects a select few mathematical ‘symbols’ (the uppercase Greek letters).

In the default configuration, lower-case Greek letters behave differently from upper-case Greek letters (the lower-case greek letters are in the maths fonts, while the upper-case letters are in the original (OT1-encoded) text fonts).

The Plain TeX solution does work, in a limited way; you set a maths style, before you start an equation; thus

does the job, but \boldmath may not be used in maths mode. As a result, this solution requires that you embed single bold characters in a text box:
$... \mbox{\boldmath$\theta$} ...$
which then causes problems in superscripts, etc. With amsmath loaded,
$... \text{\boldmath$\theta$} ...$
does the trick (and is less bad in regard to superscripts, etc), but is an unsatisfactory solution, too.

These problems may be addressed by using a bold mathematics package.

All these solutions apply to all mathematical symbols, not merely Greek letters.

Distributed as part of 2etools
Distributed as part of AMSLaTeX amslatex
Distributed as part of AMSLaTeX amslatex

This answer last edited: 2013-06-12