Abstract: In recent years, scholars have made great strides in measuring the extent of partisan gerrymandering. By and large, though, they have not yet tried to answer the questions that logically come next: What are the causes of district plans’ partisan skews? And what consequences do these skews have for democratic values? Using a unique dataset of state house and congressional plans’ partisan tilts from 1972 to the present, this Article addresses precisely these issues. It finds that single-party control of the redistricting process dramatically benefits the party in charge, while other mapmaking configurations have small and inconsistent effects. It also shows that greater black representation and greater urbanization have a modest proRepublican impact, albeit one that fades when Democrats are responsible for redistricting. It concludes as well that the harm of gerrymandering is not limited to divergences between parties’ seat and vote shares. The injury extends, rather, to the distortion of the representation that legislators provide to their constituents.