A large number of scientists are caught up in the greatly expanded and accelerated national effort in materials science and technology. The impetus for this push came largely from members of one branch of the field—the solid‐state physicists concerned with the properties of a material or the phenomena observable in a particular solid. It is, therefore, understandable that the initial emphasis of “materials science” programs stressed the solid‐state physics or “measurement of properties” aspects. Only during the last two or three years has the recognition grown beyond verbal acquiescence that in order to have a flourishing program of measuring and interpreting properties of solids, it was essential to have “good” materials. In other words, the necessity to support and develop the whole science of “materials preparation” became apparent. This note is concerned with the third stage of the development of solid‐state materials science and technology. Hardly had the effort in materials preparation been launched that it became apparent that one essential was still lacking—that which can be summarized in the expression “characterization of materials”. Some definition is in order: this term is used herein to include the whole spectrum of analyses, tests, measurements, etc., which must be carried out in order to be able to describe both accurately and precisely a particular solid. Another way of putting it is to say that it concerns the specifications necessary in order that another specimen can be established as being sensibly the same as a given model.