Realism and Neorealism are foundational theories in International Relations. They emphasize power, self-interest, and anarchy in shaping state behavior. These theories view states as primary actors in a competitive international system, prioritizing survival and security above all else. Key concepts include balance of power, security dilemma, and national interest. Realism evolved from classical thinkers like Thucydides to modern scholars like Morgenthau. Neorealism, developed by Waltz, focuses on systemic constraints. Both face criticism for neglecting non-state actors and cooperation.