This thesis attempts to explain the origin of state behavior in international politics. It compares the arguments of state level theorists who emphasize the decisive role that internal attributes, including domestic politics, political elite and regime ideology, to that of structuralists, who focus on the decisive impact of the structure of the international system. The difference is crucial: do we examine domestic politics in order to predict state behavior in international affairs or do we assume that any state, given its place in the international system, will act similarly without regard to these internal factors? The case study examined is Iran, from the early 1960s to 1989. During this period, the international system remained bi-polar, dominated by the U.S.-U.S.S.R. rivlary. The internal attributes of Iran changed radically, however, as a result of its 1979 revolution. With such a fundamental shift, state level theorists would expect a radical change in Iranian foreign policy. With the continuity of the international system, structuralists would expect essential continuity in Iran's external behavior. This thesis shows that despite rhetorical changes, Iranian foreign policy remained fundamentally the same under the Shah and the Ayatollah. The structural approach is a more useful guide to understanding state behavior.