Late time cosmic acceleration

In 1998 Type Ia supernovae observations first suggested that the recent Universe is accelerating. Further observations of Type Ia supernovae and also CMB, BAO etc. confirm the presence of a third component of Universe other than matter and radiation. Theoretically It needs new physics or modifications of earlier theory to be explained. Though the cosmological constant is the simplest solution, it has some theoretical problems. There are many alternative theories of gravity which can explain this late time acceleration. In this talk I will mainly discuss about the observation and theory of late time cosmic acceleration. First I will show how cosmological observations tell us about this kind of dynamics of the Universe and then talk about some theoretical models which can explain this acceleration. Motivations to look for alternative theories of gravity will also be discussed.