These papers discuss the problems encountered in accurate spectrophotometry and luminescence measurements of materials. They also define the status of these competences from the standpoint of basic principles, critical factors involved in the measurements, and the instrumental conditions which must be fulfilled to assure accurate measurements. Particular attention is given to the selection, production, and use of Standard Reference Materials in spectrophotometry and spectrofluorometry. Problems related to health are also covered in six of the papers, two of which include original contributions to the application of luminescence techniques to specific biochemical problems.