This paper addresses the role of prior knowledge in the comprehension of narrative and expository text, two major categories of discourse. The paper reviews some of the differences in the essence of prior knowledge required to comprehend each text type and then examines research on prior knowledge and conceptual change that deals with both text types. It concludes with a discussion of current issues and directions for further research on: (1) the nature and complexity of prior knowledge as it relates to narration and exposition; (2) the interaction of text variables and prior knowledge that make narratives or expositions easy or difficult to comprehend; (3) the effects of such components of prior knowledge as different attitudes, beliefs, social affiliations, and communication conventions on comprehension of narrative and expository text; (4) the relative importance in comprehension of exposition and narration; (5) the role of prior knowledge in relation to top-down processing concerns such as schema selection, activation, maintenance, and utilization; (6) the differences in processing demands across the two genres; (7) the role of narrative and expository text in promoting conceptual change; and (8) the role of personal involvement as a component of prior knowledge in the comprehension of narrative and expository text. Contains 79 references. (RS)