Historically, early cognitive skills have been underestimated, largely as a result of the ways these competencies have been measured, which is particularly pervasive in the area of metacognition. Only recently have researchers begun to detect evidence of contextualized metacognition in 3-5 year old preschool children through the use of observational assessment tools (e.g., Whitebread et al. "J Cogn Educ Psychol" 3:433-455, 2007, "Metacognition Learn" 4:63-85, 2009). While these observational methods are a more sensitive way to capture metacognition in young children, their exclusive use may not result in a comprehensive depiction of early metacognitive competency. In the current study, we describe the development of a metacognitive knowledge interview (McKI) and what it reveals about metacognitive processes in 43 3-5 year olds (including investigating face validity). Findings indicate that the McKI (a) is a developmentally appropriate measure for 3-5 year olds, (b) is capable of eliciting articulated metacognitive knowledge when engaging in a contextualized problem-solving task, (c) shows the expected developmental trend (i.e., older children perform at a higher level and scores increased over the course of a school year), and (d) provides sufficient variation across children. Implications for future research are discussed, including the importance of using multiple measurement tools when studying early metacognitive development.