Despite substantial policy attention to increasing the number of custodial parents with child support orders, the proportion reporting that they are owed child support is falling. Potential explanations for this include increases in shared custody, increases in the number of noncustodial parents who have low incomes (or incomes lower than the custodial parent), and growing discretion to decide whether to participate in the formal child support system. We use data on about 4,000 divorces in Wisconsin that allow us to evaluate these alternative explanations, differentiating between divorces in an earlier period (1996–98) and a later one (2004–7). A multivariate analysis and a standard decomposition approach both show that changes in custody, relative incomes, the freedom to choose child support, and other characteristics explain about half of the decline in the likelihood of orders, but about half remains unexplained. Changes in custody are particularly important in explaining the trend.