Youth out-of-school time (OST) programs and activities can provide developmental benefits for participating youth. Yet little research has examined the contextual predictors of youth OST participation. To address this issue, we examined a collection of child-, family-, school-, and neighborhood-level characteristics as predictors of OST participation using data from the Panel Study of Income Dynamics--Child Development Supplement. In summary, child and family characteristics were most useful in predicting participation such that children least likely to participate were those characterized by high levels of developmental (e.g., low achievement, behavior problems, poor health) and family (e.g., parent psychological distress and low emotional support) problems. These relations, however, emerged only during middle school and high school. For certain types of activities, namely athletics and lessons, problems measured across various contexts were more strongly associated with OST participation for higher-income families than for lower-income families. These findings point to the importance of considering multiple developmental domains and developmental periods in understanding predictors of youth OST participation. (Contains 4 tables and 6 footnotes.)