Cosmology from the polarized microwave background The polarization of the Cosmic Microwave Background (CMB) has recently had significant attention in light of results from the BICEP2 experiment. I will review CMB polarization and describe how it can be used to test cosmic inflation via gravitational wave signatures at large scales. At smaller scales it can be used both to probe the primordial universe and to extract the gravitational lensing signal that arises from the cosmic web of dark matter. I will then describe the ACTPol experiment, currently in operation in Chile. It measures the CMB polarization at high resolution and overlaps with several large-scale structure surveys that measure the universe at different wavelengths. I will show first results and discuss prospects for cosmology, including cross-correlations as a way of probing the evolution of the dark universe. I will also describe preparations for the next stage Advanced ACTPol project.