Volume 9 of Developments in Applied Spectroscopy pr e- sents a collection of tventy-three selected papers presented during the 21st Mid-America Symposium on Spectroscopy, held in Chicago, June 2-5, 1970, In general. these papers are those of the symposium type and not papers pertaining to a specific research topic that one voul expect to find in the journals. The 21st Mid-America Symposium vas sponsored by the Chicago Section in cooperation vith Cincinnati, Cleveland, Indiana, Nev England, Nev York, Niagara Frontier and Ohio Vall ey Sections of the Society of Applied Spectroscopy, and the Chicago Gas Chromatography Group. Although the Mid- America is stiIl occasionally thought of as a regional meet- ing, its attendees and authors come from all parts of the United States and Canada as vell as other countries outside North America. Both theoretieal and applied principles vere presented in sessions on emission, molecular and atomic absorption, x-ray, mass, nuclear, electron, and nuclear magnetic and electron spin resonanee spectroscopy; air and Water pOllution analyses; biomedical technology; polymers and elastomeric materials; and computer applications. The chairmen of the Symposium Committees, Mr. E. Baclavski. Dr. W. K. Baer, Mr. J. E. Burroughs, Dr. C. R. Brundle, Mr. C. Hastings, Mr. J. B. Himes, Mr. R. Isaac, Dr. R. J. Jakobsen, Mr. J. Kinder, Dr. J. L. Koenig, Mr. W. A. Loseke, Dr. R. Mattoon, Miss V. McMahon, Dr. C.E. Moore, Mr. C. S. Naiman, Dr. M. J. Oestmann, Mr. C. R.