Abstract　 　　
　 There is a fundamental question in cosmology, “Did inflation really happen?” Inflation posits that the universe grew from quantum fluctuations of the vacuum driven by negative pressure energy to expand exponentially to astronomical scales. The simplest (and therefore most compelling) versions of inflation produce a stochastic background of gravitational waves whose amplitude depends only on the energy scale at which inflation occurred. The gravitational waves imprint a polarization pattern on the CMB (B-mode polarization), that then provides a direct way to measure the energy scale of inflation. In this talk, I will present the Cosmology Large Angular Scale Surveyor (CLASS) project. It is an experiment with an unprecedented ability to detect the B-mode polarization to the level of r (the tensor to scalar ratio) ≤ 0.01. It consists of 4 ground-based wide-field polarimeters, operating at 40, 90 and 150 GHz. CLASS will measure the large angular scale CMB polarization signature by observing ~65% of the sky above 45 degrees elevation from the Cerro Toco in the Atacama desert of northern Chile, 5180 meters above sea level.