If you have any interest in mathematics at all, you will enjoy this book. Like all of Stewart's books on mathematics, this is well-written, understandable, and interesting. The intended audience would be high-school students who are thinking about majoring in mathematics, college students who are majoring in mathematics, and the rest of us who wish we were smart enough to have majored in mathematics.
Stewart talkes broadly about what the fields of math involve, including some philosophy of mathematics, which is a fascinating field in its own right. He provides advice on what its like to study math, teach math, and above all, DO math.
The only downside of this book is the high price (in the bookstore) for such a small book. PolymathInTraining practiced unaccustomed frugality by reading this entire book in the bookstore for the price of a cup of coffee. But I will purchase it when it is released in paperback.