The Activity Theory Model involves five main principles:
- Hierarchical Structure of Activity: The unit of analysis is an activity directed at an object, which motivates activity, giving it a specific direction. Activities are composed of goal-directed actions that are undertaken to fulfill the object. Actions are implemented through automatic operations, which do not have their own goals; rather, they provide an adjustment of actions to current situations. Activity Theory holds that the constituents of activity are not fixed, but can dynamically change as conditions change.
- Object-Orientedness: Human beings live in a reality that is objective in a broad sense. The things that constitute this reality have not only the properties that are considered objective according to natural sciences but socially/culturally defined properties as well.
- Internalization and Externalization: Activity Theory differentiates between internal and external activities. It emphasizes that internal activities cannot be understood if they are analyzed separately from external activities, because they transform into each other. Internalization is the transformation of external activities into internal ones. Internalization provides a means for people to try potential interactions with reality without performing actual manipulation with real objects (mental simulations, imaginings, considering alternative plans, etc.). Externalization transforms internal activities into external ones. Externalization is often necessary when an internalized action needs to be "repaired," or scaled. It is also important when collaboration between several people requires their activities to be performed externally in order to be coordinated.
- Tool Mediation: In a broad sense, Activity Theory emphasizes that human activity is mediated by tools. Tools are created and transformed during the development of the activity itself and carried with them in a particular culture - historical remains from their development. So, the use of tools is an accumulation and transmission of social knowledge. Tool use influences the nature of external behavior and also the mental functioning of individuals.
- Development: Activity Theory is a general research methodology. The basic research method in Activity Theory is not traditional laboratory experiments, but the formative experiment that combines active participation with monitoring of the developmental changes of the study participants. Ethnographic methods that track the history and development of a practice have also become important in recent work.