Volume 6 of Developments in Applied Spectroscopy presents a collection of twenty-eight selected papers from those that were pre- sented at the Eighteenth Mid-America Symposium on Spectroscopy held in Chicago, May 15 to 18, 1967. In general, the papers selected by the editors are those of the symposium type and not those papers pertaining to a specific research topic that one expects to be sub- mitted to a journal. Not all of the submitted papers were included. Some revisions could not meet the deadline and others were not accepted based on the advice of the reviewers. It is the opinion of the...