Worksite health promotion programs have become increasingly prevalent in the United States, and one or more health promotion programs are found in two-thirds of all private worksites with 50 or more employees. Reasons for recent growth in program frequency include increased concern for worker health, rapidly escalating employer payments for health care benefits to workers, and growing evidence of a strong linkage between employee health and productivity. Published results of evaluations to date suggest that worksite health promotion programs can have positive impacts on health behaviors and health status. In addition, economic analyses are suggesting that some programs can affect the slope of health care costs and have the potential of high cost-effectiveness compared to some clinical interventions. A number of research challenges remain, particularly understanding the influences of the worksite environment and how employee health promotion programs affect individual and organizational productivity.