This book has pretty much anything you could want about the theory of cyclotomic fields: Fermat's Last Theorem(See how it was done before Wiles!), an introduction to iwasawa theory, and a proof of Thaine's theorem for those of you who are interested in Mihailescu's proof of Catalan's conjecture. One thing though, this book is not really an introduction. If you're not familiar with Algebraic Number Theory and p-adic analysis, you will be completely lost in this book. It definitely doesn't hurt to know at least the major statements of Class Field Theory. Other than that, though, a truly great book!