Several training situations have been devised in which animals have to base their discriminative behavior upon cues that terminate within a trial before they have the opportunity to make the correct response. The correct response must be guided by the memory of those cues, and the subject must generally ignore the memory of relevant stimuli from preceding trials. This situation necessitates the action of a working memory within each trial. It is the purpose of this chapter to review the conceptual status of working memory, especially in relation to other kinds of memory processes; to describe a few working memory procedures; to give an account of research on working memory in pigeons carried out in our laboratory; and to speculate upon an appropriate theoretical account of our results.