This paper summarizes the theoretical basis of the relationship between preconceptions and the construct of mental effort in order to identify factors that researchers have shown to influence mental effort, and to suggest an agenda for future research in this area. It begins with a discussion of the theoretical bases of the relationship between preconceptions and mental effort which reviews and summarizes four theories of cognition and motivation: (1) reactive theory; (2) active processing theories; (3) curiosity theory; and (4) attribution theory. It is also noted that past experiences, perceptions of the task, and characteristics of the media may each contribute to the preconceptions that learners bring to an instructional setting, and may in turn influence the invested mental effort. The paper then describes research on preconceptions and mental effort in the specific areas of learner preconceptions; mental effort and learning; the influence of the perceived task on mental effort; and the influence of characteristics of the media on mental effort. The paper concludes with suggestions for future research, which include measuring the delay time in responding to some secondary task while attending to the primary task of reading or viewing the stimulus material; studying the role of embedded post-questions in text using a secondary task technique to measure the amount of cognitive capacity used during processing; and using other methods to increase the cognitive capacity used in processing a text-based lesson. (38 references) (CGD)