A common prescription for reducing the number of uninsured is to increase the tax subsidization of health insurance in the U.S. Yet, we already provide over $100 billion per year in tax subsidies to health insurance. This paper provides an assessment of the past and potential impacts of taxation on health insurance coverage and costs. I begin by reviewing the central facts on health insurance and taxation. I then provide a framework for assessing the impacts of tax policies on health insurance coverage and costs, and I review the existing empirical evidence on the key behavioral parameters required to model these impacts. I conclude with the policy implications of these findings for tax policies to expand insurance coverage.