  We study the generalization of S-duality and Argyres-Seiberg duality for a
large class of N=2 superconformal gauge theories. We identify a family of
strongly interacting SCFTs and use them as building blocks for generalized
superconformal quiver gauge theories. This setup provides a detailed
description of the ``very strongly coupled'' regions in the moduli space of
more familiar gauge theories. As a byproduct, we provide a purely four
dimensional construction of N=2 theories defined by wrapping M5 branes over a
Riemann surface.
