Health care payers in the United States and abroad have used wellness incentives as a tool to improve health and reduce costs. In Germany, public insurers operate many such programs. Participation nearly doubled between 2004 and 2008, reaching one-quarter of the publicly insured population. An evaluation of one large wellness program there found that it reduced costs. However, population-level survey data also suggest that individuals with low incomes or poor health are less likely to enroll. In the United States, the Affordable Care Act raised the maximum allowed size of wellness incentives, which could lead to wide differences in insurance premiums between users and nonusers of programs, and may risk reintroducing a form of medical underwriting. The German experience confirms the cost-saving potential of programs, but also suggests that they should be evaluated rigorously to ensure they do not disadvantage those with health problems or low incomes.