This paper will present the current staus of solar cells fabricated from CuInGaSe@2@(CIGS) polycrystalline thin films. CIGS thin film solar cells are considered as an excellent option for power generation at low cost. The technology has matured to the point of commercial production. We will highlight the special properties of CIGS materials and the 3-stage growth process developed at NREL. We have achieved a world-record solar cell efficiency of 19.3% at NREL. As the device efficiencies have increased and the confidence in the repeatability has grown, more attention is given to basic science of junction formation, surface properties of absorber films, and electronic properties of interfaces. We shall review our work in this area and also our collaborations with our industrial partners.