Marketing has become one of the most influential forces in contemporary market economies. Yet despite its ubiquitous empirical presence, uncountable textbook definitions, and sixty years of scholarly work, a coherent sociological understanding of this powerful concept is still lacking. Drawing on Luhmannian social systems theory, historical analysis, and four qualitative studies, the author theorizes on the marketing function as a self-contained system of communications. It is argued that marketing systems prosper within a host organization if and as long as they successfully influence observers' preferences towards particular brands. On these conceptual foundations, a comprehensive brand- and communication-centered theory is developed that fulfills Alderson's, Cox's, and Bartels' foundational requirements for a general theory of marketing in an unprecedented way.