  Glueballs and other resonances with large gluonic components are predicted as
bound states by Quantum Chromodynamics (QCD). The lightest (scalar) glueball is
estimated to have a mass in the range from 1 to 2 GeV/c**2; a pseudoscalar and
tensor glueball are expected at higher masses. Many different experiments
exploiting a large variety of production mechanisms have presented results in
recent years on light mesons with J(PC) = 0(++), 0(-+), and 2(++) quantum
numbers. This review looks at the experimental status of glueballs. Good
evidence exists for a scalar glueball which is mixed with nearby mesons, but a
full understanding is still missing. Evidence for tensor and pseudoscalar
glueballs are weak at best. Theoretical expectations of phenomenological models
and QCD on the lattice are briefly discussed.
