Advocates of mail ballot elections predict that voting by mail will produce higher turnout and allow voters to become more informed. Our study tests these predictions by taking advantage of a “natural experiment” in which many California voters are assigned to vote by mail because they live in less populous precincts. By matching these mail ballot precincts with traditional polling place precincts that contain voters with similar demographic characteristics, we are able to observe the effects of voting by mail on comparable groups of voters taking part in the same elections.