Internalization (or internalisation) is the process of making something internal, with more specific meanings in various fields. It is the opposite of externalization.

Psychology and sociology explore the concept of internalization, which refers to the integration of attitudes, values, standards, and opinions into one's own identity. Internalization plays a crucial role in learning, moral development, and the formation of the super ego. Early socialization and internalized values can shape a child's moral character and future behavior. A child developmental study found that children who internalized parental rules and showed empathy tended to perceive themselves as more moral and were rated by parents and teachers as more competent and adaptive.

Internalization is also relevant in behavioral psychology, where it can refer to disorders and behaviors that are not externally evident, such as depression, anxiety disorder, bulimia, and anorexia. In other fields, internalization has various meanings, such as endocytosis in biology, the practice of multinational enterprises in economics and management, and executing orders from a firm's own inventory in finance.