The topic of this book – the role of trust funds in American national budgeting – lies at the intersection of public policy and political science. This is not an accident. My graduate training at Berkeley was in both fields. At Berkeley's Graduate (now Goldman) School of Public Policy, I studied the efficient and equitable design of public policies. After I returned to Berkeley for doctoral studies in political science (having spent two years as a legislative aide in Washington), I became interested in the historical and institutional context in which policymaking unfolds, and in the impact of past choices on present and future options. My interest in federal trust funds was originally stimulated by my inability to make sense of contemporary political debates over Social Security. I noticed that whenever lawmakers discussed the relationship between Social Security and the federal budget, they focused on the spending and income flows of the Social Security Trust Fund. But what was the significance of this arcane fiscal device? If, as I soon discovered, the Social Security Trust Fund was not money under the mattress, what governance roles did the device perform? Answering that question took me rather far afield – back to Social Security's adoption and very early development, and to other policy sectors, such as transportation, where the trust fund mechanism is also employed. The common thread was the attempt by current policy actors to put future budget actors under obligation.