Etasub(c) as we know it

Various theoretical models for paracharmonium are critically reviewed. The main emphasis is but on the dispersion approach which has proved to be powerful enough to fix, say, the etasub(c) mass, msub(etac) = (3.00 +- 0.02) GeV. A few original remarks concerning mainly the radiative transitions in charmonium are included. In particular, a new, simple, and reliable method for calculating Gamma(J/psi → etasub(c)γ) is described which makes no reference to potentials, overlap integrals, etc. (orig.)