  Glueballs are particles whose valence degrees of freedom are gluons and
therefore in their description the gauge field plays a dominant role. We review
recent results in the physics of glueballs with the aim set on phenomenology
and discuss the possibility of finding them in conventional hadronic
experiments and in the Quark Gluon Plasma. In order to describe their
properties we resort to a variety of theoretical treatments which include,
lattice QCD, constituent models, AdS/QCD methods, and QCD sum rules. The review
is supposed to be an informed guide to the literature. Therefore, we do not
discuss in detail technical developments but refer the reader to the
appropriate references.
