Interstellar medium (ISM) dust grains are only about 1% of the mass of the ISM, but they have very important role in the formation of stars. ISM dust grains originate from the material ejected by stars. Presence of dust grains in ISM is revealed by interaction with starlight. They absorb roughly 30-50% of the starlight emitted by the Galaxy and re-radiate it as far-infrared continuum emission. The interstellar extinction curve has a lot of spectral structure in the form of absorption and emission by discrete components arising from the dust grains. The leading materials for dust grains are silicates and carbonaceous material with ices of volatile compounds like water or carbon dioxide condensed on their surfaces forming mantles. Wavelength dependence of interstellar extinction and polarization are the main source of information on dust grains. Different models of dust grains were proposed based on observed phenomena of interstellar extinction and interstellar polarization. In this talk, I will discuss about interstellar extinction curve, properties of dust grains and different models on dust grains highlighting their alignment mechanism.