Activity theory and its concept of expansive learning are examined with the help of four questions: 1. Who are the subjects of learning? 2. Why do they learn? 3. What do they learn? 4. How do they learn? Five central principles of activity theory are presented, namely activity system as unit of analysis, multi-voicedness of activity, historicity of activity, contradictions as driving force of change in activity, and expansive cycles as possible form of transformation in activity.