Geometry defines the world around us, helping us make sense of everything from architecture to military science to fashion. Euclid's Elements is arguably the most influential book in the history of mathematics. Berlinski provides a concise homage to this elusive mathematician and his staggering achievements, and shows that, for centuries, scientists and thinkers have relied on Euclid's axiomatic system, a method of proof still taught in classrooms around the world.