An expert talk was delivered by Prof. K N Pathak on Born - Oppenheimer Approximation. This talk opens the discussion of many body problems one studies in Condensed Matter Physics and Nuclear Physics. It is the first major approximation taken to simplify the unsolved many body problems. The assumption that the electronic motion and the nuclear motion in molecules can be separated allows us to write the total wave function as product of electronic part and nuclear part. The journey to unveil the secret of many body Physics was started today via this basic talk. Many more interesting talks are lined up to happen.