This NBER series presents current academic research findings in the areas of taxation and government spending. The papers included provide important background information for policy analysts in government and the private sector without making specific policy recommendations. This twenty-first installment in the series reports on recent research concerning both taxation and social insurance policy. The papers discuss Medicaid's implicit tax on the benefits of private long-term care insurance, an alternative to current unemployment insurance systems, the tax treatment of health insurance expenditures, the effective marginal tax rates on labor supply and saving, and the rationale for and effect of energy-related tax policies.James M. Poterba is Mitsui Professor in the Department of Economics at MIT. He has been Director of the NBER Public Economics Research Program since 1991 and has edited volumes 6-20 of Tax Policy and the Economy.