This volume presents some of the papers from the 15th Mid-America Symposium on Spectroscopy held in Chicago on June 2-5, 1964. The Mid-America Symposium is sponsored annually by the Chicago Section of the Society for Applied Spectroscopy, in cooperation with the St. Louis, Niagara Frontier, Cleveland, Detroit, Indianapolis, and Milwaukee sections of the Society and the Chicago Gas Chromatography Discussion Group. Although basically a regional meeting, the Symposium continues to draw enthusiastic attendance from coast to coast and numerous foreign countries. The present volume contains 45 of the 110 papers presented at the Symposium. It is with some misgiving that we offer this volume as the proceedings of the meeting with less than half of the total papers included. However, it is the opinion of the Symposium Committee that publication of the excellent material available from the Symposium provides a valuable addition to the literature in the field of spectroscopy. Response to previous volumes of this series seems to verify this opinion. As Chairman of the Symposium and Editor of this volume, I express my sincere appreciation to the authors whose manuscripts make up this volume. I also extend my gratitude to the following members of the Symposium Committee whose time and effort made the 15th Mid-America Symposium a success. Mr. Russell J. Hansen, Exhibits; Mr. Robert L.