The complex activity of human is a fundamental element of any economy, including a digital one. In connection with the above, the development of methodological aspects of integrated activities is an urgent task. The methodological basis of the research is a system analysis, as well as the theory of multi-agent systems. The main trends distinguishing the “digital” economy from “non-digital” one are highlighted based on the systematic approach. The concept of complex activity (CA) is defined and the ontology of the basic concepts of CA methodology is offered. An integrated and coordinated system of CA models is introduced: the basic model of the structural element of activity (SEA), which is the main atomic element of CA representation and analysis; logical model of CA, reflecting the structure of the objectives of the activity and the hierarchy of subordination of elements of the CA; causal model of CA …