The aim of this book is to formulate and justify a social theoretical foundational position, which is referred to here as reductive individualism, following a formulation by Max Weber. This position consists of reducing types of human interaction to understandable actions, meaning it exclusively focuses on the actions of the individual participants involved. Such a program stands in contrast not only to the holistic perspective in the tradition of Émile Durkheim but also to systems theory, to approaches that understand collective practices as meaning- and action-generating, as well as to a powerful variant of individualism itself, known as structural individualism. In relation to all these positions, reductive individualism can be presented as a compelling alternative.