This study examines time-use for outdoor recreation during 1965 to 2007. Using data on over 47,000 individuals from six nationally representative time-use surveys, we first document time-use trends between 1965 and 2007. We then develop a two-part instrumental variable censored regression model (a hurdle model) to predict individual-level time-use. Our results show that per capita time-use in outdoor recreation has more than doubled since 1965. This long-term increase was driven largely by increased participation rate. However, in the last decade or two, per capita time-use in outdoor recreation has stayed constant or slightly decreased. This change was driven mostly by reduced time-use by active participants; participation rate has not changed considerably. Demographics, amount of leisure, and other factors all have contributed to changes over time, but their effects and relative importance vary between participation, time-use per active participant, and time periods.