The science of 'theranostics' plays a crucial role in personalized medicine, which represents the future of patient management. Over the last decade an increasing research effort has focused on the development of nanoparticle-based molecular-imaging and drug-delivery approaches, emerging as a multidisciplinary field that shows promise in understanding the components, processes, dynamics and therapies of a disease at a molecular level. The potential of nanometer-sized agents for early detection, diagnosis and personalized treatment of diseases is extraordinary. They have found applications in almost all clinically relevant biomedical imaging modality. In this review, a number of these approaches will be presented with a particular emphasis on MRI and optical imaging-based techniques. We have discussed both established molecular-imaging approaches and recently developed innovative strategies, highlighting the seminal studies and a number of successful examples of theranostic nanomedicine, especially in the areas of cardiovascular and cancer therapy. Nanotechnology is starting to invade different areas of science and 'theranostic' biomedical science is no exception [1][2][3][4]. The science of theranostics plays a critical role in personalized medicine, which represents the future of patient management. Nanoparticle-based medicinal approaches have emerged as an interdisciplinary area, that shows promise in understanding the components, processes, dynamics and therapies of disease at a molecular level. The unprecedented potential of nanoplatforms for early detection, diagnosis and personalized treatment of diseases have found application in every biomedical imaging modality.These include noninvasive cellular and molecular-imaging techniques, including ultrasound (US) [5], optical [6], PET [7], computed tomography [8][9] and MRI [10][11][12][13][14].MRI is a noninvasive diagnostic technique based on the interaction of nuclei with each other and the surrounding molecules in a tissue. The sensitivity of magnetic resonance is low in comparison to nuclear and optical modalities; however, the absence of radiation (transmitted or injected) and high spatial resolution (e.g., sub-millimeter) makes it advantageous over Correspondence to: Gregory M Lanza,