  In this talk the pomeron conjecture is reviewed and constituent gluon models
are derived. In a simple two-gluon glueball spectrum the pomeron trajectory and
the daughter trajectories are computed. The open problems of two-gluon
glueballs are discussed, including transversality and Yang's theorem, the spin
tensor interactions, the structure of the string and decays. The related
systems of charmed hybrids and of the gluelump are also addressed. To conclude,
different aspects of glueballs that could be measured at PANDA are highlighted.
