We examine how the growth in vote-by-mail and changes in voting technologies led to changes in the residual vote rate in California from 1990 to 2010. In California’s presidential elections, counties that abandoned punch cards in favor of optical scanning enjoyed a significant improvement in the residual vote rate. We also conduct the first analysis of the effects of the rise of vote-by-mail on residual votes. Regardless of the election, increased use of the mail to cast ballots is robustly associated with a significant rise in the residual vote rate.