Gluon Mass, Glueballs and Gluonic Mesons

We review the phenomenological and theoretical evidences for dynamical gluon mass generation and the main features of the glueball spectrum in (pure gauge) Yang-Mills theories. The mixing between glueball and conventional $\bar{q}q$ states in $f_0$ scalar mesons is discussed. For pseudoscalar mesons, the inclusion of the glue field in an effective low energy theory is presented leading to a third isoscalar ${\eta }^{\mathrm{\prime }\mathrm{\prime }}$ partner of the $\eta$ and ${\eta }^{\mathrm{\prime }}$. Branching ratios for processes involving ${\eta }^{\mathrm{\prime }\mathrm{\prime }}$ are given and, when available, compatible with data for $\eta (1405)$.