e, The Story of a Number by Eli Maor. 1994, ISBN 0-691-03390-0. This is a good book. I have read it twice now. The number "e" has the approximate value of 2.7182818284..., but cannot be written down precisely because it is an irrational number. This book covers a wide variety of topics related to "e", from the invention of logarithms, to "e" and complex numbers. The book doesn't assume the reader knows calculus, however calculus level math is discussed and explained.