The biology of living skeletal muscle and the processes which occur during its conversion to meat are critical to an understanding of quality in muscle-based foods. There is a variety of animal species from which muscle foods are obtained. Although some species-specific differences exist, the changes associated with the conversion of muscle to meat are essentially the same. Slaughter of livestock generally involves stunning, exsanguination, removal of hide, hair, or feathers, evisceration, and washing. In commercial plants, these procedures are accomplished in less than 1 h. Onset of rigor mortis varies from 3 to 6 h in smaller animals such as poultry, and 24–36 h in large animals like cattle. Commercial harvesting of fish may be accomplished in a variety of ways. In large operations, fish are caught, skinned, scaled or shelled, eviscerated, filleted, and stored frozen within 1 h of harvest. In smaller operations, boats may harvest fish and store these on ice until further processing when the boat reaches port.