There are a wide variety of psychographic and edumetric tests but none capture the totality of what it means to be a systems thinker. At this time systems thinking not only has popularity but also promises to address the complex problems we face today. It is therefore necessary to identify how to measure systems thinking on a continuum of mastery. The advent of DSRP Theory makes the variables that need to be measured explicit. We present herein a brief review of psychographic and edumetric advances in cognition, metacognition, and systems thinking, and then detail the development and validation of the Systems Thinking and Metacognition Inventory (STMI).