High Tc Superconductivity:. Symmetries and Reflections

This is a talk given at the Symposium "Symmetries and Reflections", dedicated to Prof. C. N. Yang's retirement. In this talk, I shall reflect on my personal interaction with Prof. Yang since my graduate career at SUNY Stony Brook, and his profound impact on my understanding of theoretical physics. I shall also review the SO(5) theory of high T_c superconductivity and show how my collaboration with Prof. Yang in 1990 led to the foundation of this idea.