On Election Day in 2010 and again in 2012, we collaborated with Facebook to deliver a message encouraging their users to vote. Subsequently, we matched Facebook records to voter records to estimate the effect of this get-out-the-vote treatment. In both elections, we show that there was a direct effect - users who saw the message were more likely to vote. Additionally, we show that a larger number of people were induced to vote through indirect effects - they were made more likely to vote through close friends receiving the message.