In 1991, Foster began compiling research on his major life's work, a book about the history and evolution of fiat paper currency. He took a break to publish his first book, The Lost Stamps of the United States (1993). Designed to help children learn history and geography, it was widely acclaimed, and even approved for classroom use by the California Department of Education. Foster next embarked on a series of book signings and classroom presentations.

Yet the passion to bring forth the history of fiat paper money remained. With his shop located just a block from the U.C. Berkeley campus, Foster has had access to its renowned library system, as well as the opportunity to discuss fiat monetary systems with countless foreign travelers and students. Combined with the efforts of several dedicated and talented research assistants, the project went ahead at full steam. In 1995 he began working with Paul Myslin, who was then pursuing an English degree at the University. Drawing on his own lifelong interest in the subject matter, Myslin joined the effort to make the book both a storehouse of knowledge and accessible to the average reader. Over sixteen years of meticulous research and revision have gone into Fiat Paper Money‹The History and Evolution of Our Currency.