In theory, workplace wellness programs offer an important public health and policy opportunity to improve the health of the working population, encourage prevention, and lower the cost of healthcare. However, the success of these programs is highly dependent on the level of participation, the effect on health claims costs, on medical utilization, and the resulting decrease in health risk behaviors as a result of participation in the program. This three-paper dissertation evaluates a workplace wellness program in California that uses a financial incentive to recruit people to participate. The study is a two-year observational cohort study utilizing data provided by Blue Shield of California Health Insurance Plan from their Healthy Lifestyle Rewards (HLR) program. Demographic, claims, and medical utilization data from a subset of 8,003 participants in 2006 and 2007 are compared with a control group of non-participants. Program exposure and Wellness Assessment survey data is available for a subset of the participating population. Paper 1 evaluates the determinants of employee participation and retention in the program from 2006 to 2007. The analysis finds that lower-income and high-risk employees have greater odds of participating in HLR as compared to high-income employees. Participation in HLR is significantly related to medication usage for two chronic conditions: high cholesterol, and depression. Paper 2 evaluates the effect of participating in HLR on health care utilization and medical claims. The results find that participation in HLR in 2006 was associated with significant declines in all measures of outpatient utilization (including non-institutional physician and non-physician claims, and physician visits) in the following year. There were no significant effects on claims spending for cholesterol and depression medications, or in utilization in the categories of emergency department visits, and inpatient admissions. HLR may serve as a substitute for some forms of outpatient physician and non-physician care, most likely acting as an informational resource. Paper 3 evaluates the impact of participating in HLR on modifiable health risks. The results find that the use of specific HLR help modules is associated with a significant improvement in many biometric and health risk factors. Participants in HLR exercised more frequently, consistently ate more fruits and vegetables, and reported lower stress levels. Overall, it is found that HLR reduces health care expenditures and decreases medical utilization without a detectable effect of negative health behaviors or increased health risks. These findings suggest that promoting workplace wellness programs may be a promising component of comprehensive health care reform.