PI - this seemingly mundane number-holds a world of mystery, which has fascinated mathematicians from ancient times to the present. What is PI? What is the real value of PI? How do mathematicians determine the value of PI? In what ways is PI used? How was it calculated in ancient times? Its elusive nature has led investigators over the years to ever-closer approximations. In this delightful introduction to one of math's most interesting phenomena, Drs Posamentier and Lehmann review PI's history from prebiblical times to the twenty-first century and the many amusing and often mind-boggling attempts to estimate its precise value. They show how this ubiquitous number comes up when you least expect it, such as in the calculation of probabilities and in biblical scholarship. In addition, they present some quirky examples of obsessing about PI over the centuries--including an attempt to legislate its exact value, and even a PI song--as well as useful applications of PI in everyday life. Among its many attributes, mathematicians call PI a `transcendental number' because its curious value cannot be calculated by any combination of addition, subtraction, multiplication, division, or square root extraction. More curious still, regardless of the number of decimal places to which you extend the value of PI, the decimal never repeats itself. In 2002 a Japanese professor using a supercomputer calculated the value to 1.24 trillion decimal places! Nonetheless, in this huge string of decimals there is no periodic repetition. This enlightening, intriguing, and stimulating approach to mathematics will entertain and fascinate readers while honing their mathematical literacy.