'A Materialist Social Theory of the Idea' advances a unified theoretical framework for understanding how ideas emerge, circulate, and materialize in the world. Rejecting both classical Idealism and reductive Materialism, the book develops a neuromaterialist approach that defines ideas as physically instantiated patterns of neural activity and traces their effects across social, institutional, and material domains. Beginning from the premise that thought is a biological process, the book follows the idea from its origin in the brain through its transmission via language and behavior, its reproduction within culture, and its eventual crystallization in norms, institutions, and physical structures. This recursive process—linking brain, behavior, environment, and social organization—provides a comprehensive model of how ideas function as causal forces in history. Drawing on insights from sociology, philosophy, neuroscience, and political theory, the work introduces original conceptual tools, including models of ideational transmission, activation, and threshold dynamics, as well as the concept of cognitive terraforming to describe the large-scale transformation of reality through ideation. This book offers an interdisciplinary framework for analyzing ideology, social change, and institutional development, making it relevant to scholars and students in social theory, sociology, philosophy of mind, and related fields. It also provides a foundation for further research into the material basis of thought and its role in shaping human behavior and social structure.