The purpose of this article is to provide an introduction to the growing body of research on the development of scientific reasoning skills. The focus is on the reasoning and problem-solving strategies involved in experimentation and evidence evaluation. Research on strategy use in science has undergone considerable development in the last decade. Early research focused on knowledge-lean tasks or on tasks in which subjects were instructed to disregard prior knowledge. Klahr and Dunbar (1988) developed an integrated model of scientific discovery that has served as a framework to study the interaction of conceptual knowledge and the set of cognitive skills used in scientific reasoning. Researchers now take a more integrated approach, examining the development and use of strategies in moderately complex domains in order to examine the conditions under which subjects' theories (or prior knowledge) influence experimentation, evidence evaluation, and belief revision. Recent findings from integrated studies of scientific reasoning have the potential to inform and influence science education and conceptualizations of science as both academic skill and content domain. © 2000 Academic Press.