Numbers enter our lives in every way and have powerful significance in describing our world and thought by many as possessing mystical and even magical properties. The book considers the early development of numbers and the special numbers of pi and phi (the golden number) and the consequences of Fibonacci's famous series. It looks at the constants of gravity, the velocity of light and Avogadro's number. The contributions made by many famous philosophers are traced: Galileo, Kepler, Newton, Einstein, Hoyle and Martin Rees. Chapters on applications to Telecommunications, Electromagnetic waves and Einstein's revolutionary contribution including E = mc2 are included together with a survey of our Solar System and potential hazards we may meet. It concludes with "just six numbers," numbers which can be thought as defining not only our world but the whole universe: its formation and future.