  This is a contribution to the review "50 Years of Quantum Chromdynamics"
edited by F. Gross and E. Klempt [arXiv:2212.11107], to be published in EPJC.
The contribution remembers the early searches and explains how to find a
glueball, based on its properties. The results of a coupled-channel analysis
are presented that provides evidence for the scalar glueball and first hints
for the tensor glueball. Data on radiative decays of $\psi(2S)$ and
$\Upsilon(1S)$ show scalar intensity that is likely due to glueball production.
