During the last 30 years, a series of experiments were carried out at
CERN in order to prove the existence of glueballs, i.e. hadrons without
valence quark content . After motivating double-pomeron-exchange as a
relevant production process, the first part of the talk will briefly
review methods and results. In the second part, one recent analysis of
COMPASS data will be followed step by step as an illustrative example.