Professor Wilson, in an active research career spanning more than 5O years at Harvard University, became a chief architect of chemical physics. He provided definitive theoretical treatments of many aspects of molecular vibrational and rotational dynamics, especially symmetry analysis, and developed with his students key experimental methods in infrared and microwave spectroscopy. The 40 papers reprinted in this volume include many classics offering Wilson's insight and lucid exposition. Commentary by the editor sets the papers in historical context and traces connections to much work descended from the seminal contributions of Wilson.