  This paper summarizes experimental results presented at the international
conference honoring Prof. C.N. Yang's 80th birthday. I show seven examples that
illustrate how one can use angle-resolved photoemission spectroscopy to gain
insights into the many-body physics responsible for the rich phase diagram of
cuprate superconductors. I hope to give the reader a snapshot of the evolution
of this experimental technique from a tool to study chemical bonds and band
structure to an essential many-body spectroscopy for one of the most important
physics problems of our time.
