Autophagy is a catabolic process in which autophagic lysosomes degrade most cytoplasmic contents. Autophagy is usually activated in the absence of nutrients and is associated with many physiological and pathological processes, including growth, differentiation, neurodegenerative diseases, infections and tumors. Light chain 3 (LC3) is a widely recognized autophagy marker. There are three isoforms of the LC3 protein (LC3A, LC3B, and LC3C) in mammals. They undergo post-translational modifications during autophagy. The LC3 protein is first cleaved by Atg4 at its carboxy terminus immediately after synthesis to produce LC3-I, which is localized in the cytoplasm. During autophagy, LC3-I is modified and processed by a ubiquitin-like system including Atg7 and Atg3 to produce LC3-II with a molecular weight of 14 kD and localized to autophagosomes. The magnitude of the LC3-II/I ratio can be used to assess the level of autophagy.