Nanocarriers have drastically changed the face of health care by making a mark in diverse arenas of diagnosis, drug delivery, and gene delivery to name a few. The recent feat in nanotechnology has been the birth of nanotheranostics which aims at blending both therapeutic and diagnostic functions within a single nanoscaffold. The field of theranostic nanomedicine is a result of fruitful advances in fields of material science, imaging modalities, formulation development, and molecular biology. Theranostic nanomedicine that was at first developed for enhancing the quality of treatment meted out to cancer patients has now been explored even in atherosclerosis and infections, albeit to a lower extent. The review summarizes various types of nanocarriers that have been explored with one or sometimes multiple imaging modalities for an array of applications ranging from drug delivery and gene delivery to photosensitizing agent delivery for photodynamic therapy. The article also highlights the few but significant developments made in the field of theranostic nanomedicine for atherosclerosis and infections. In conclusion, theranostic nanomedicine is a rapidly growing field. However, there are a few problems that need to be addressed before theranostic nanocarriers carve a niche for themselves in the clinic.