Many people see an effective preventive AIDS vaccine as the best solution to the HIV/AIDS pandemic. Ten years ago many scientists had hoped that a vaccine would be available by now. Most scientists are still optimistic that vaccines will be developed and many candidates are being tested....

Behaviors that are putting people's health and well-being at risk are widespread in the developing world and some of them, like smoking and unhealthy diets, are on the rise. Some of these behaviors can be prohibited or prevented by taxation. But financial incentives such as conditional cash...