  We use photo-electron paramagnetic resonance (EPR) measurements and
first-principles calculations to identify and explain the properties of carbon
in AlN. We present clear evidence for carbon substitution on the nitrogen site
(C$_{\rm N}$). We also clarify the origin of a widely observed EPR spectra in
AlN that, although often attributed to a deep donor defect, we demonstrate is
surprisingly due to C$_{\rm N}$. Finally, we show the presence of C$_{\rm N}$
is consistent with the absorption spectra at 4.7 eV observed in AlN.
