  Glueballs are bound states in the spectrum of quantum chromodynamics which
consist only of gluons. They belong to the group of exotic hadrons which are
widely studied experimentally and theoretically. We summarize how to calculate
glueballs in a functional framework and discuss results for pure Yang-Mills
theory. Our setup is totally self-contained with the scale being the only
external input. We enumerate a range of tests that provide evidence of the
stability of the results. This illustrates the potential of functional
equations as a continuum first-principles method complementary to lattice
calculations.
