Nanoscience deals with the materials and technologies based on them in the size range of 1-100 nm. The definition is indeed slippery. The nanoworld indeed is a weird border between the realm of individual atoms and molecules (where quantum mechanics rules) and the macroworld (where the bulk properties of materials emerge from the collective behaviour of trillions of atoms such as a steel beam). Although the existence of nanoscience can be traced both in living and non-living things existing in nature since billions of years, however, the recent and intense interest in nanomaterials and structures stem from the fact that they may boast superior and novel chemical, physical and biological properties, phenomena and processes. The development of new tools (STM, AFM, etc.) that have made characterization and manipulation of nanostructures practical and also as a result of new methods for the preparation nanosized structures and materials together with their tremendous scope of applications make nanoscience as one of the most advanced areas in science and technology. In the present paper, an overview is given on various aspects of nanomaterials including classification, approaches for synthesis and characterization, properties arising due to reduced dimensions, size confinement, interfacial phenomena, application areas, challenges, etc.