This book is the first in a series of discussions about the great minds in the history and theory of finance. While the series will address the contributions of significant individuals to our understanding of financial decisions and markets, this first in the series begins by establishing a framework upon which all subsequent discussions rest. This first volume begins by describing how individuals make decisions over time, and why these decisions change as we age and our circumstances change. The work of these financial theorists created the basis for what we now know as personal finance. In turn, these theorists answered for us the following six questions. Why do people save? How does inflation affect savings? Why do additional savings not always translate into new investment? How does a household's savings pattern change over its lifetime? Why is the national savings rate quite volatile over the business cycle? Likewise, why are individual savings also volatile? We answer these questions through the context of the lives of Irving Fisher, John Maynard Keynes, Franco Modigliani, and Milton Friedman. The lives of each of the individuals treated in this volume become extraordinary, not because they made an unfathomable leap in our understanding, but rather because they looked at something in a different way and caused us all to forever look at the problem in this new way. That is the test of genius.