On 20 Aug 2013, at 13:00, Matt Gushee <matt@gushee.net> wrote:

I don't think it's the font. I have been trying to produce an em dash
using the latest stable release from contextgarden.net, with a couple
of different fonts--Alegreya, which is a free OpenType font, Latin
Modern, and one other that I don't remember. In my case, regardless of
the font, \emdash works but --- does not.

Thanks! I can confirm that \emdash works perfectly with the minimal example I posted.