14. Iwasawa theory for modular forms
The Kubota–Leopoldt picture of Parts I and II is the Iwasawa theory of
\GL(1): Dirichlet characters are the algebraic automorphic forms for
\GL(1), and \zeta_p is their p-adic L-function. The next case is
\GL(2), whose automorphic forms are modular forms. Remarkably, all of the
\GL(1) theory has a \GL(2) analogue for sufficiently nice modular forms,
although the picture is not yet complete in full generality. This chapter
records the three constructions and the comparison theorems that bind them.