Italian mathematician Leonardo of Pisa (c. 1170-c. 1250, who was also known as Fibonacci, or “son of Bonacci,” although some historians say there is no evidence that he or his contemporaries ever used the name) brought the idea of Arabic notation and the concept of zero to Europe. His book *Liber abaci (The Book of the Abacus)* not only introduced zero, but the arithmetic and algebra he learned in Arab countries. Another book, *Liber quadratorum* (or *The Book of the Square)* was the first major European advance in number theory in a thousand years. He is also responsible for presenting the Fibonacci sequence. (For more information about Fibonacci and the Fibonacci sequence, see “Math Basics.”)