OBJECTIVE: The purposes of this article are to summarize the basic concept and the strategies of reporter imaging; introduce reporter genes frequently used in optical imaging, nuclear medicine, and MRI for in vivo application; and show typical examples of reporter gene imaging. CONCLUSION: In molecular biology, many reporter genes have been developed for monitoring cellular processes. Development of controlled gene delivery systems promotes construction of various types of reporter genes for monitoring the level of a gene expression, promoter activity, and protein-protein interaction. When an imaging reporter gene is placed under the control of a promoter, the amount of reporter protein can be dynamically visualized in vivo. Instrumental advances in molecular imaging have increased the sensitivity and resolution of in vivo reporter imaging. Though several types of reporters and multimodal imaging instruments are currently available, more efficient multimodal reporter gene systems and detectors compatible with several imaging modalities are needed.