Cosmic Microwave Background (CMB) is the cleanest signal from the early phase of the universe. One believes this is intrinsically isotropic, un-polarized
and has a blackbody spectrum. Hence any deviation from these features provides a very good handle to understand the physical phenomenon both at the surface of last scatter and after that epoch as the photons of
CMB travels towards us. The talk will essentially highlight some of the physical processes in the Universe which can produce these deviations.