A Ree group is a twisted Chevalley group constructed by combining a field automorphism
with an exceptional symmetry of a root system that
interchanges long and short roots in certain Lie algebras.
The two families are
for
and
for
, where
.
Their group orders are
and
The groups in both families are simple apart from their smallest members. In particular, is not simple, and the derived subgroup of
is the simple Tits group.