Of the various meat properties, which impact its quality, tenderness is the most important for the consumer. During the post mortem conversion of muscle to meat, a complex process of meat tenderization occurs. For a long time now, researchers in this field of science have been particularly interested in the mechanism of meat tenderization. Despite intensive studies, the crux of those processes is not thoroughly recognized. In the review paper, main theories are presented, which refer to the mechanisms of meat tenderization, both the non-enzymatic (calcium theory of meat tenderization, effect of osmotic pressure) and the enzymatic theories (processes including proteolytic endogenous enzymes: calpains and calpastatin, caspases, cathepsins, proteasomes, and matrix metalloproteases). The enzymes in question are likely to be engaged in the post mortem proteolysis of muscle proteins. Moreover, potential markers are discussed of different metabolic pathways that participate in developing the post mortem meat tenderness.