Epistemic cognition is the thinking that people do about what and how they know. Education has long been concerned with promoting reflection on knowledge and processes of knowing, but research into epistemic cognition began really in the past half century, with a tremendous expansion in the past 20 years. This review summarizes the broad range of psychological and education research that comprises the study of epistemic cognition, and it identifies various fault lines that currently prevent coherent synthesis of theoretical models and empirical findings. The fault lines include differences in how scholars conceptualize knowledge and cognition, and the contextual nature of epistemic cognition, with consequent differences in accounts of individual development, as well as in research methods. In the coming century, research that can integrate findings among individual, situative, and cultural accounts of cognition may enable the advancement of coherent models of epistemic cognition and its development and support improved educational efforts aimed at such development.