  Many models beyond the Standard Electroweak Theory, top-down or bottom-up,
contain extensions of the gauge symmetry group by extra U(1)' factors which can
be understood or treated as subgroups of E(6). A brief overview of such models
is followed by a sketch of a systematic classification. We then describe how
the resulting extra massive neutral gauge bosons can be searched for and in
case of positive evidence diagnosed using electroweak and collider data.
