The influences that demographic changes may have on the design of private pension plans in the twenty-first century are examined. Major demographic factors to be considered include the aging of the population, declining mortality rate, potential for an even lower mortality rate, improved health for all ages and especially for older workers, and improvements in labor productivity. Possible changes in the objectives of private pension plans are considered, including those related to changes in public policy, employer attitudes, and the health care system. Implications of federal regulatory trends are also discussed. Current pension plan coverage is outlined, and the likely future impact of tax benefit changes and retiree health care coverage are noted. The fundamental pension plan design question, whether to shape the plan in the form of a defined benefit plan or a defined contribution plan, or a combination, is considered in the context of trends since 1975. Advantages of each design approach are enumerated. Two additional issues discussed are the target age of retirement and inflation protection. (MSE)