This text on a central area of number theory covers p-adic L-functions,
class numbers, cyclotomic units, Fermat's Last Theorem, and Iwasawa's
theory of Z_p-extensions. This edition contains a new chapter on the
work of Thaine, Kolyvagin, and Rubin, including a proof of the Main
Conjecture, as well as a chapter on other recent developments, such as
primality testing via Jacobi sums and Sinnott's proof of the vanishing
of Iwasawa's f-invariant.