  In this talk, delivered at the Oscar Klein Centenary Symposium in Stockholm,
I review the 1938 conference held in Warsaw devoted to \lq \lq New Theories in
Physics". I review all of the talks presented at this meeting and discuss in
detail Klein's paper where he proposed a unified model of electromagnetism and
the nuclear force that foreshadowed the later developments of non-Abelian gauge
theories.
