It might seem strange to ask whether increasing access to medical care can improve children's health. Yet Lindsey Leininger and Helen Levy begin by pointing out that access to care plays a smaller role than we might think, and that many other factors, such as those discussed elsewhere in this issue, strongly influence children's health. Nonetheless, they find that, on the whole, policies to improve access indeed improve children's health, with the caveat that context plays a big role--medical care "matters more at some times, or for some children, than others." Focusing on studies that can plausibly show a causal effect between policies to increase access and better health for children, and starting from an economic framework, they consider both the demand for and the supply of health care. On the demand side, they examine what happens when the government expands public insurance programs (such as Medicaid), or when parents are offered financial incentives to take their children to preventive appointments. On the supply side, they look at what happens when public insurance programs increase the payments that they offer to health-care providers, or when health-care providers are placed directly in schools where children spend their days. They also examine how the Affordable Care Act is likely to affect children's access to medical care. Leininger and Levy reach three main conclusions. First, despite tremendous progress in recent decades, not all children have insurance coverage, and immigrant children are especially vulnerable. Second, insurance coverage alone doesn't guarantee access to care, and insured children may still face barriers to getting the care they need. Finally, as this issue of "Future of Children" demonstrates, access to care is only one of the factors that policy makers should consider as they seek to make the nation's children healthier.