As already said, some of the applications presented in this review are probably too detailed with regard to the crudeness of the non-relativistic model which is assumed. On the other hand, some qualitative conclusions very likely will hold beyond the NRQM, for instance the regularities of the mass spectrum in flavour space, a consequence of the universality of the interquark potential.
Beyond ordinary mesons and baryons, a key issue in hadron spectroscopy is the existence of multiquark states. The main difficulty lies in extrapolating the interquark forces from the qq and qqq sectors to more complicated systems. Another difficulty will be to treat correctly the four-body (or five-, or six-body) problem, with, in particular, a proper account for the coupling to the dissociation channels. It is hoped that this introduction to three-body techniques will serve as a training ground for checking or improving multiquark calculations, in the same way as the recent refinements on the two-body systems have been a source of progress for the three-body problem.