Inflation is a compelling theory that describes the process of Big Bang. Many predictions of inflation theory have been confirmed by observations of cosmic microwave background (CMB) over the last decade. A most exciting, yet unobserved prediction of inflation is the production of a scale-invariant gravitational wave background, which would leave a distinct imprint of “B-mode” polarization in the CMB. I will describe the physics behind this prediction, our ongoing effort to search for this signal with the BICEP program at the South Pole, and the outlook for the next decade.