Pole mass renormalon and its ramifications

I review the structure of the leading infrared renormalon divergence of the relation between the pole mass and the MS ¯ mass of a heavy quark, with applications to the top, bottom and charm quark. That the pole quark mass definition must be abandoned in precision computations is a well-known consequence of the rapidly diverging series. The definitions and physics motivations of several leading renormalon-free, short-distance mass definitions suitable for processes involving nearly on-shell heavy quarks are discussed.