  A common feature of Coxeter groups and right-angled Artin groups is their
solution to the word problem. Matthew Dyer introduced a class of groups, which
we call Dyer groups, sharing this feature. This class includes, but is not
limited to, Coxeter groups, right-angled Artin groups, and graph products of
cyclic groups. We introduce Dyer groups by giving their standard presentation
and show that they are finite index subgroups of Coxeter groups. We then
introduce a piecewise Euclidean cell complex $\Sigma$ which generalizes the
Davis-Moussong complex and the Salvetti complex. The construction of $\Sigma$
uses simple categories without loops and complexes of groups. We conclude by
proving that the cell complex $\Sigma$ is CAT(0).
