As the opening authors at a two-day seminar concerned with imaging techniques, we have a responsibility to define some terms. Obviously, "imaging" is the first word that merits consideration. The dictionary (Ref. 1) associates many words with an image, including imitation, likeness, copy, and conception. A definition (Ref. 1) that seems to fit many of the topics to be discussed here is as follows: "An image is an optical appearance or counterpart of an object---analogous to an image formed by light rays." A definition such as this permits us to include test systems that employ light as well as other radiations (X- and y-rays, neutrons, acoustical, ultrasound, and thermal) in our image seminar. Indeed,a glance at the program quickly verifies that the majority of test systems to be discussed involve radiation other than light.