*The Elements of Euclid* (c. 300B.C.E.) has been the most enduring and influential mathematical work of all time. In it, the ancient Greek mathematician presented the work of earlier mathematicians and included many of his own innovations. The *Elements* is divided into thirteen books: the first six cover plane geometry; seven to nine address arithmetic and number theory; ten treats irrational numbers; and eleven to thirteen discuss solid geometry. In presenting his theorems, Euclid used the synthetic approach, in which one proceeds from the known to the unknown by logical steps. This method became the standard procedure for scientific investigation for many centuries, and the *Elements* probably had a greater influence on scientific thinking than any other work.