Molecular imaging is leading an important role in the era of molecular medicine. Optical imaging, a rising star in the filed of molecular imaging, largely consists of fluorescent imaging and bioluminescent imaging. In the fluorescence imaging, an illuminating light excites fluorescent reporters in the living subject, and a charged coupled device (CCD) camera collects an emission light of shifted wavelength. In the bioluminescent imaging, reporter genes code for the luciferase that is responsible for fireflies' glow. After the injection of the substrate luciferin, animals carrying the luciferase gene are imaged with a super-sensitive CCD camera to pick up the small number of photons transmitted through tissues. It has been shown that well-aimed and creatively built reporters let researchers explore and answer a lot of biologically important questions in living subjects. Despite its relatively short history, optical imaging is rapidly being implemented in various clinical areas as well as research fields.