The Balanced Budget Act of 1997 established federal grants to the states to create the State Children's Health Insurance Program (SCHIP). This presented the states with a number of implementation choices concerning administrative models for the new programs, as well as choices about eligibility standards,enrollment simplification, crowd-out, and cost sharing requirements. At the same time, the states were also implementing welfare reform. We describe the most important of these implementation choices, and using data from the Current Population Survey, we estimate the impacts of state policy on enrollment in this multiprogram environment. The results indicate that SCHIP programs that are administered as Medicaid expansions are more successful than either separate SCHIP plans or combination programs in enrolling children. States that remove asset tests and implement presumptive eligibility and self-declaration of income have higher enrollment levels. Continuous eligibility and adoption of mail-in applications have no effect on overall enrollment. Waiting periods and premiums reduce enrollment. Stringent welfare reform reduces children's enrollment, despite federal policy that was intended to protect children from the consequences of welfare reform. The negative impacts of a number of these policy reforms substantially reduce enrollment,potentially offsetting the more favorable impacts of other policy choices. We estimate that if all states adopted the policy options that facilitate program use, enrollment for children with family incomes less than 200 percent of the poverty line could be raised from the current rate of 42 percent to 58 percent.