A model is proposed for memory that stresses a distinction between episodic memory for encoded personal experience and semantic memory for abstractors and generalizations. Basically, the model holds that questions influence the nature of memory representations formed during instruction, and that memory representation controls the way in which stored knowledge can be used. The paper is divided into three major sections. In the first section various proposed typologies of questions are described, to identify the dimensions along whcih questions may vary and to describe both the utility and inadequacies of current typologies. It is argued that an instructionally useful taxonomy must be based upon consideration of the empirical effects of questions, and that development of such a taxonomy is a fundamental goal of research on levels of questions. In the second section the limited research on levels of questions is reviewed, to integrate what is known and not known about the effects of asking different types of questions during instruction. Both deficiencies in the existing studies and promising directions for future research are indicated. The third section briefly presents the information-processing model of knowledge acquisition and attempts to relate question-level effects to the model. (Author/CTM)