This volume traces the evolutionary roots of political ideology by examining empirical associations among genetics, endocrinology, neurophysiology, life history strategies, personality factors, and other individual difference variables. This first chapter introduces and explains Multilevel Selection Theory, an indispensable theoretical framework capable of organizing all subsequent chapters as they variously review political ideology’s evolution, both as an abstract feature of mind and as a contextual feature of society. From this vantage point, one can see how selection operates across at least the following four different levels of biological aggregation: (1) genes; (2) neurophysiology; (3) individual phenotypes; (4) groups. Genetic differences are the substrate of neurobiological differences that collectively inform those behavioral differences described as moral emotions, temperament, or personality, all of which comprise part of an organism’s behavioral phenotype. These behavioral differences affect survival and reproduction. But this does not happen in a vacuum. As genes act within the confines of organisms, organisms act within the context of groups. While groups are not tangible, as are organisms, they are nonetheless aggregations with emergent properties fully capable of affecting the survival and reproduction of individuals, and their underlying genetics.