This paper is an attempt to develop some concepts and objectives to use as theoretical basis for the descriptive cataloging of pictures. Although the basic objectives to be met when describing books and pictures are similar, the means used to achieve these objectives may be different. The purpose of developing a theoretical basis for picture cataloging is to provide the reader with the means of evaluating, adapting, and applying presently existing codes and formats, or for devising new codes and formats; this paper does not attempt to construct an actual code, nor to present methodical evaluations of present practices.