This book is about numbers and so many questions relating to them. What is the nature of numbers? Are they discovered or invented? What is mystical about them? Mathematicians develop a hierarchy of numbers in which mysterious dichotomies appear. For example, the integer 5 is not the same as the rational 5 which in turn is different from the real 5. The author explains how this conceptual maze does not affect the layperson's arithmetic. He also discusses such fascinating topics as primes, perfect numbers, inaccessible numbers and many other unsolved problems relating to the treacherous terrain of infinity, which have baffled mathematicians and philosophers alike.