Al Cuoco is Senior Scientist and Director of the Center for Mathematics Education at Education Development Center. He taught high school mathematics to a wide range of students in the Woburn, Massachusetts public schools from 1969 until 1993. He currently spends a lot of time at Lawrence, MA High school. At EDC, he has worked in curriculum development, professional development, and education policy. A student of Ralph Greenberg, he received a Ph.D. from Brandeis in 1980, with a thesis and research in algebraic number theory. His favorite publication (except for this book) is his 1991 article in the American Mathematical Monthly, described by his wife as “an attempt to explain a number system no one understands with a picture no one can see.