Integration, Ayn Rand wrote, "is the key to man's consciousness, to his conceptual faculty, to his basic premises, to his life." This lecture examines the key to integration: the identification of essentials. It presents a detailed "chewing" of the crucial role of essentials in the mental act of integration. Some issues discussed are: the reason man must think in essentials; the relationship between principles and essentials; context and essentials; the function of essentials in both forming and applying concepts.