  This review is based on the talk in the conference of "Spectroscopic Studies
on Molecular Chirality" held on Dec 20-21 2013. The objects of the present
paper are to (1) derive the energy difference between Laevorotatory, or
left-handed, (L-) and Dextrotatory, or right-handed, (D-) molecules and to (2)
discuss how this tiny energy difference leads us to the observed enantiomer
excess. Relations with other parity violating phenomena in molecules, electric
dipole moment and natural optical activity, are also discussed.
