The in vivo fluorescent and bioluminescent imaging systems are a promising method. There has been a growing interest in applying these optical imaging approaches to study different disease process and complex biology in vivo. In this laboratory, we applied the fluorescent imaging systems to study the roles of carcinogenesis and cancer metastasis in vivo. The in vivo fluorescent and bioluminescent imaging allows quantitative and qualitative visualization of the cell function as well as microenvironment. The in vivo optical imaging systems will be a powerful technique in cancer biology.