Meat colour is a very important visual sensory attribute that influences purchasing decisions. Post-mortem muscle is biochemically active and any deviation from the ultimate post-mortem muscle pH can influence meat colour. More specifically, changes in pH can affect the key determinants of meat colour such as metmyoglobin reduction, oxygen consumption, and lipid oxidation. Recently, much research focus has been on the role of mitochondria in meat colour. The use of ‘omics’ technologies such as genomics, proteomics and metabolomics will help to better understand biochemical changes occurring during the conversion of muscle to meat. This chapter will discuss factors affecting beef colour, key biochemical reactions that influence beef colour and the role of mitochondria in beef colour.