Imaging nanoprobes are a group of nano-sized contrast agents devised for providing improved contrast and spatial resolution for bioimaging. Among various imaging nanoprobes, optical nanoprobes capable of monitoring biological events or progresses in the cellular and molecular levels have been developed for early detection, accurate diagnosis, and personalized image-guided treatment of diseases. The optical activities of nanoprobes can be tuned on demand for specific applications by engineering their size, surface nature, morphology, and composition. In addition, by virtue of the nanostructure, nanoprobes have displayed favorable pharmacokinetic features and target specificity reflecting clinical demands. In this review, we focus on typical approaches and recent trends in development of nanoprobe-mediated optical imaging and their potential as a clinical diagnostic modality.