Abstract: Autophagy is a lysosome-mediated cellular self-digestion process that participates in the dynamic recycling of damaged organelles and long-lived proteins. Within the body, it plays a significant role in maintaining homeostasis and in tumorigenic processes. Autophagy ensures that cells can obtain sustained energy under stress conditions, such as nutrient deficiency and the tumor microenvironment, thereby maintaining their internal balance and survivability. Autophagy is not only dependent on the environment, cell type, and tumor stage, but is also regulated by the interaction between tumor cells and their microenvironment. Autophagy can inhibit tumorigenesis in the early stage of cancer; however, it promotes tumorigenesis and increases tumor cell growth and metastasis in the later stage. This article reviews the mechanism of autophagy and its role in the proliferation and development of tumor cells. In-depth understanding of the role of autophagy in cancer biology will facilitate the design of new drugs and clinical translational studies targeting autophagy-related molecules for anti-tumor therapy.