The cellular degradation process is highly regulated and plays critical roles in cell physiology. Autophagy is the major degradation process. Thirty years ago I found by light microscopy that yeast induces massive protein degradation within the vacuole under nutrient starvation. Electron microscopy revealed that membrane dynamics of this process are similar to macroautophagy in mammals. Then many autophagy-defective mutants were successfully obtained. 18 Atg proteins, required for the autophagosome formation, consist of six functional units, including a protein kinase complex, the PI3 kinase complex and two unique conjugation systems. The identification of ATG genes completely changed the landscape of autophagy research. Manipulation of these genes unveiled a truly broad range of physiological functions of autophagy. Autophagy plays important roles not only in nutrient recycling, but also intracellular clearance through the elimination of harmful proteins and damaged organelles. Now it is becoming clear that autophagy is relevant to many diseases and health problem.