Autophagy (eating oneself) is the lysosomal degradation of cytosolic components, usually the long-lived proteins and organelles, and recycle the digested food for cellular metabolism during starvation. Hence, autophagy is functionally involved in cell development, immunity, tissue remodeling and cell adaptation to the adversary circumstances. Recently it suggests that autophagic machinery plays a critical role in protecting eukaryotes from infection of microbial infections, the process called xenophagy. The genetic basis of the intracellular digestioin was highlighted, and physiological and pathophysiological regulation of autophagy is discussed.