Of all the meat traits, tenderness is considered to be the mostimportant with regard to eating quality (Miller, Carr, Ramsey,Crockett, & Hoover, 2001). It appears that the main determinantof ultimate tenderness is the extent of proteolysis of key targetproteins within muscle fibres (Koohmaraie & Geesink, 2006;Taylor, Geesink, Thompson, Koohmaraie, & Goll, 1995a). Giventhe recognised importance of proteolysis in the tenderisationprocess this review has focused on the biochemistry of enzymesystems that have a potential role in the process, and some ofthe experimental evidence either rejecting or supporting theirinvolvement. Our research in this area has focused on the fundamental biochemical aspects of the potential proteolytic systemsinvolved tenderisation in pigs therefore the majority of theresearch described in this review focuses on this species, however,the scope of this review has been extended to cover fundamentalobservations made in other species.