Despite the fact that over 200 phosphorylation sites have been mapped on the mitochondrial oxidative phosphorylation (OxPhos) complexes, very little is known about the relevant cell signaling pathways and the terminal kinases and phosphatases that control these phosphorylations. Within OxPhos, cytochrome c (Cytc) plays a special role because it is not only involved in electron transport but is also a key executor of apoptosis when it is released from the mitochondria. In this book the authors present further research on the study of cytochrome C as well as cytochrome B. Some of the topics discussed in the book include the regulation of cytochrome C in respiration as well as its role in apoptosis. It also focuses on the structural aspects and touches base on cytochrome B5 as a pleiotropic metabolic modulator.