Abstract: Since quasars were first recognized as cosmological sources their relation to galaxies has been a puzzle. We now know that quasars are powered by accretion of gas onto supermassive black holes at the centers of massive galaxies. What continues to elude our understanding is the impact that quasars have on their host galaxies. Recent numerical simulations suggest that quasars can drive powerful gas outflows that ultimately bring about an end to star formation and black hole activity. I will discuss observations designed to directly test this hypothesis. Because gas outflows are challenging to observe in the presence of a bright quasar, our study focuses on a sample of galaxies that are a few 100 million years past the peak of their star formation and black hole activity. In these 'post-starburst' galaxies we find evidence for outflowing cool gas with velocities upwards of 1000 km/s. We consider the energetics of the gas and argue that quasars play a significant role in removing gas from galaxies and quenching star formation.