Inorganic nanoparticles are considered to possess very high surface to volume ratios, exhibit quantum size effects, at nanoscale they are thermodynamically stable as compared to metastable bulk systems, and regulated by kinetics of nanoparticles. They possess unique physical properties, especially surface effects are quite dominant. The properties of nanoparticles in terms of brittleness, hardness, plasticity, elasticity all of them explain the mechanical stability of the nanomaterials. The catalytic efficiencies of nanoparticles are also very appreciable. Moreover, the optical properties of the nanoparticles help in various applications of such particles in biosensing, drug-delivery, photothermal and photodynamic therapy. The resonant dielectric nanostructures lower the radiation losses and are quite stable leading to different applications such as actuators and sensing systems. The magnetic properties of nanoparticles lead to its superparamagnetic behavior, thus efficient enough in hyperthermia and magneto- thermal therapies. In this chapter, a special discussion on metal sulfides, especially molybdenum sulfides, has been done followed by a special note on perovskite oxides.
