The notions of actor (although not all the theories discussed here use this exact term) and interaction are central for the authors of the theories reviewed in this chapter. It is not the properties of the humans that are prominent in these works but the interpersonal positioning that guides their relations, the way in which they interact in complex surroundings (network, action system, activity system, sign system, etc.) and the social dynamics that result. The four theses examined here are alike in many ways. Unlike critical approaches and certain institutionalist approaches their analysis does not include the effects of social superstructures. In these cases there are no external determinants, no overarching social influence. The accent is on the autonomy of the actors who have the means (construction of meaning, power to act, strategic capacity) that grant them the free space they exploit.