A three-level model of cognitive processing to account for complex monitoring when individuals are faced with ill-structured problems, i.e., problems on which opposing or contradictory evidence and opinion exists, is proposed. At the first level, cognition, individuals compute, memorize, read, perceive, solve problems, etc. At the second, metacognitive level, individuals monitor their own progress when they are engaged in these first-order tasks. At the third level, epistemic cognition, individuals reflect on the limits of knowing, the certainty of knowing, and criteria of knowing. Epistemic assumptions influence how individuals understand the nature of problems and decide what kinds of strategies are appropriate for solving them. While cognitive and metacognitive processes appear to develop in childhood and are used throughout the life span, current research on adult reasoning suggests that epistemic cognitive monitoring develops in the late adolescent and adult years.