The aging of the US population will be a primary domestic public policy issue during the next decades. According to Census Bureau projections, the proportion of the elderly in the total population will increase while the proportion of working-age population is projected to decline. These demographic changes imply a significant growth in the number beneficiaries in major federal entitlement programs. Existing program rules and rapidly escalating health care costs are expected to lead to fiscal pressures and pose challenges for economic growth. In most countries with advanced economies, the problem is far more severe. The challenges of coping with an aging population require action in the near term to forestall more difficult choices in the long term. This book provides an assessment of the forces that drive government spending on retirees, examines how the retirement and health care of older citizens might be financed and measures the potential impact of different reform proposals. Probabilistic forecasts and comparative analyses enhance the impact of policy reform.