This paper examines the role of institutions in integration of human activity across the levels of its hierarchical system. In the perspective of System-Activity Methodology, human activity is viewed as the only primary reality. Human activity is completely defined by standards. The main process constituting human activity is self-reproduction. The system of activity comprises four hierarchical levels ordered by relation of inclusion and defined by corresponding types of standards: (1) universe of mass activity – by universal values, (2) spheres of mass activity – by corresponding institutions, (3) organizations of collective activity – by schedules and protocols, and (4) acts, performed by individuals, – by modes of action. Enabled by their structure that mirrors the hierarchical system of activity, institutions integrate this hierarchical system of activity in a “top-down” manner. Actualization of the institutional standards proceeds in the opposite direction and integrates levels of activity in a “bottom-up” manner. The usual occurrence of deviations require supplementary remedial and sanctioning activities that penetrate all hierarchical levels and, in turn, create bottom-up pressure to change institutional standards at all levels. The two-way integration results in tight interdependence of the hierarchical levels of the activity system, necessitating consideration of the entire hierarchical context, if one is to understand and effectively act upon activity systems of any scale.