Metacognitive theories are systematic frameworks that explain and direct cognition, metacognitive knowledge, and regulatory skills. This paper proposes a framework for understanding people's theories about their own cognition. It distinguishes tacit, informal, and formal metacognitive theories, discussing their differences using criteria from developmental literature. The paper also considers the origin and development of these theories and their implications for educational research and practice. Metacognition is widely recognized, but there is debate about its scope and meaning. The paper aims to explore how individuals integrate different types of metacognitive knowledge and regulatory skills into systematic cognitive frameworks called metacognitive theories. It distinguishes specific components of metacognitive knowledge (e.g., conditional knowledge) and regulation (e.g., comprehension monitoring) from their systematic integration (e.g., theoretical knowledge about variables affecting cognitive performance). The paper proposes that individuals construct metacognitive theories for two reasons: (a) to systematize their metacognitive knowledge, and (b) to understand and plan their own cognitive activities within a formalized framework. The paper is divided into four sections. The first reviews traditional accounts of metacognition, distinguishing between metacognitive knowledge and regulation. The second provides a taxonomy of metacognitive theories, ranging from tacit models of cognition to formalized theoretical structures. The third section considers how individuals construct metacognitive theories. The final section examines methodological and educational implications of the analysis. Metacognitive knowledge includes three types: declarative, procedural, and conditional knowledge. Declarative knowledge refers to knowing "about" things, procedural knowledge refers to knowing "how" to do things, and conditional knowledge refers to knowing the "why" and "when" aspects of cognition. Understanding these components helps in developing systematic metacognitive theories that guide cognitive activities.Metacognitive theories are systematic frameworks that explain and direct cognition, metacognitive knowledge, and regulatory skills. This paper proposes a framework for understanding people's theories about their own cognition. It distinguishes tacit, informal, and formal metacognitive theories, discussing their differences using criteria from developmental literature. The paper also considers the origin and development of these theories and their implications for educational research and practice. Metacognition is widely recognized, but there is debate about its scope and meaning. The paper aims to explore how individuals integrate different types of metacognitive knowledge and regulatory skills into systematic cognitive frameworks called metacognitive theories. It distinguishes specific components of metacognitive knowledge (e.g., conditional knowledge) and regulation (e.g., comprehension monitoring) from their systematic integration (e.g., theoretical knowledge about variables affecting cognitive performance). The paper proposes that individuals construct metacognitive theories for two reasons: (a) to systematize their metacognitive knowledge, and (b) to understand and plan their own cognitive activities within a formalized framework. The paper is divided into four sections. The first reviews traditional accounts of metacognition, distinguishing between metacognitive knowledge and regulation. The second provides a taxonomy of metacognitive theories, ranging from tacit models of cognition to formalized theoretical structures. The third section considers how individuals construct metacognitive theories. The final section examines methodological and educational implications of the analysis. Metacognitive knowledge includes three types: declarative, procedural, and conditional knowledge. Declarative knowledge refers to knowing "about" things, procedural knowledge refers to knowing "how" to do things, and conditional knowledge refers to knowing the "why" and "when" aspects of cognition. Understanding these components helps in developing systematic metacognitive theories that guide cognitive activities.