While Americans are spending an increasing amount of leisure time engaged in online activities, total leisure time has remained constant since at least 2003. This paper uses data from the American Time Use Survey from 2003-2010 to investigate the extent to which online leisure is substituting for other leisure activities. The analysis suggests that online leisure, especially online video and social networking, appears to come at the expense of watching traditional television, socializing, and relaxing. However, the net crowding out effect is incomplete—each minute of online leisure is correlated with 0.27 minutes less of other leisure—suggesting that at least some online leisure occurs concurrently with other, offline, leisure. Nevertheless, both the amount of time engaged in online leisure and the magnitude of the (negative) correlation between online and offline activity are increasing, suggesting that online activities are taking the place of a growing share of offline leisure activities. Additionally, some evidence suggests that new online activities also crowd out previous online activities. In particular, online leisure is increasingly negatively correlated with time spent on personal email.