String theory and cosmology

There is increasing evidence for a period of accelerated expansion or inflation in the very early universe. Most inflationary models are sensitive to ultra-violet properties of the underlying fundamental theory, including quantum gravity effects, so it makes sense to explore inflationary model building in the context of a UV complete framework. I discuss recent ideas about inflation in string theory, and describe some striking consequences of the simplest models. I also outline how, with simple and conservative assumptions, one can argue that there is a ``landscape'' of string vacua which encompasses diverse possibilities for low-energy physics.