Theoretical background The poster gives an overview of the research and theoretical background of an ongoing dissertation project the major focus of which is on metacognition in mathematics education. A central objective is the documentation of metacognition during mathematical activity in prospective mathematics university students and using the results of this study to expand upon existing category systems of metacognition-especially for the field of Calculus. Metacognition is generally understood as knowledge about and cognitive processes dealing with (one's own) knowledge and cognitive processes (Flavell, 1976) as well as regulating those. Metacognition is usually divided into a declarative and a procedural component and their respective sub-categories. Declarative metaknowledge signifies available, explicable knowledge a person possesses about the workings of their own cognitive functions and knowledge. Further specifying the concept, declarative metaknowledge can be subdivided into the three categories person knowledge, task knowledge and strategy knowledge. Procedural metacognition on the other hand is focused on planning, cognitively monitoring, reflecting and evaluating cognitive activity as well as regulating the latter. (Schneider, 2010) It is expected here that in order to be metacognitively active during mathematical learning or problem-solving processes two or more of these (and possibly further) subcategories "interact".