Herbert P. Ginsburg has been fascinated with children’s thinking since his undergraduate years. He was amazed (and still is) by young children’s minds—their thinking, their strategies, their distinctive ways of understanding the world. Very early in his teaching career, he interviewed children about their thinking, videotaped the interviews, and discussed them with his students, who seemed to benefit greatly. He engaged in this kind of pedagogy for some 50 years (and still thinks that it works!) at Cornell University, the University of Rochester, and Teachers College, Columbia University, where he was the Jacob Schif Foundation Professor of Psychology and Education. His research has focused on the development of mathematical thinking in children around the world (including Africa and East Asia). Using what he learned from this research (and the research of others, including some wonderful students), he helped to develop a math curriculum for little children, interactive storybooks/games, methods for assessing young children’s math knowledge, and guides to reading story books to young children. He also consulted with various television shows, which gave him the opportunity to meet Blue and Team Umizoomi, as well as Big Bird (in person!) and his Sesame Street creators. He had a deep mathematical conversation with the Count. He hopes you will enjoy and learn from this book.