  In this article we review the theory of cosmological inflation with a
particular focus on the beautiful connection it provides between the physics of
the very small and observations of the very large. We explain how quantum
mechanical fluctuations during the inflationary era become macroscopic density
fluctuations which leave distinct imprints in the cosmic microwave background
(CMB). We describe the physics of anisotropies in the CMB temperature and
polarization and discuss how CMB observations can be used to probe the
primordial universe.
