Today's pension policies can affectretirement incomes and the public finances for decades tocome. Retirement income systems that are affordable today,will often prove unsustainable in the future, given the twinpressures of demographic aging and the maturing of pensionschemes. The World Bank's pension reform optionssimulation toolkit (PROST) models pension contributions,entitlements, system revenues, and system expenditures overa long time frame. The model is designed to promote informedpolicymaking, bridging the gap between quantitative andqualitative analysis of pension regimes. It is a flexible,computer-based toolkit, easily adapted to wide range ofcountries' circumstances.