Internalization refers to the active attempt to transform an extrinsic motive into personally endorsed values and thus assimilate behavioral regulations that were originally external. A taxonomy of motivations have been described based on the degree to which they are internalized.
Intrinsic motivation refers to initiating an activity because it is interesting and satisfying in itself to do so, as opposed to doing an activity for the purpose of obtaining an external goal (extrinsic motivation). Key studies that led to emergence of SDT included research on intrinsic motivation. Research applying SDT to different areas in social psychology and education has increased considerably since the 2000s. Deci and Richard Ryan wrote a book titled " Self-Determination and Intrinsic Motivation in Human Behavior" that SDT was formally introduced and accepted as a sound empirical theory. In the 1970s, research on SDT evolved from studies comparing intrinsic and extrinsic motives, and from growing understanding of the dominant role that intrinsic motivation played in individual behavior. SDT focuses on the degree to which human behavior is self-motivated and self-determined.
It is concerned with the motivation behind choices people make without external influence and interference.
Self-determination theory ( SDT) is a macro theory of human motivation and personality that concerns people's inherent growth tendencies and innate psychological needs.