Imaging advances human gene therapy by providing noninvasive assessment in living subjects. The modalities most applicable for gene therapy include gamma-ray, optical, and magnetic resonance (MR) imaging and MR spectroscopy. Importantly, imaging can be used to validate the efficacy of gene therapy and to measure levels and locations of transgene expression. Further, the capability to temporally follow induced gene expression in the same subjects is highly advantageous. Genetic-based reporters have demonstrated the capability of imaging gene transfer in vivo. Strategies include systemic administration of a radioactive agent that accumulates at the location of gene expression, followed by nuclear imaging, as well as several optical imaging approaches based on fluorescence. The purpose of this chapter is to provide an overview of current and emerging technologies, review how imaging has been applied to assess adenoviral-based gene therapy in humans, and discuss genetic-based imaging reporter systems.