  This is a summary of some of the basic facts about flat 2-orbifold groups,
otherwise known as 2-dimensional crystallographic groups. We relate the
geometric and topological presentations of these groups, and consider
structures corresponding to decompositions of the orbifolds as fibrations or as
unions. We also consider covering relations, and record the bases of Seifert
fibrations of 4-manifolds with geometries of solvable Lie type.
