2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/49664In this review I cover recent developments concerning the construction of non-relativistic effective theories for perturbative heavy quark-antiquark systems and heavy quark mass definitions. I then discuss next-to-next-to-leading order results on quarkonium masses and decay, top quark pair production near threshold and QCD sum rules for $Υ$ mesons.22 pages, LaTeX, Contribution to the 8th International Symposium on Heavy Flavour Physics, Southampton, UK, 25-29 July 1999High Energy Physics - Phenomenologytext