The authors investigate the potential of Health Savings Accounts (HSAs) to expand health insurance coverage. They examine how many currently uninsured people might be encouraged to buy coverage through HSAs, and what the impacts of such actions might be on the group and nongroup health insurance markets. Their main conclusions: HSAs are not likely to be an important contributor to expanding coverage among uninsured people because most of them do not face high-enough marginal tax rates to benefit substantially from the tax deductibility of HSA contributions. Meanwhile, HSAs could potentially destabilize the small-group market. To the extent that they encourage well-compensated healthy workers to abandon job-based coverage—a result that is more likely if current HSA provisions are combined with proposed premium deductibility—HSAs could undermine the entire structure of job-based coverage among small firms.