Complex interdependence in international relations and international political economy is a concept put forth by Robert Keohane and Joseph Nye in the 1970s to describe the emerging nature of the global political economy. The concept entails that relations between states are becoming increasingly deep and complex. These increasingly complex webs of economic interdependence undermine state power and elevate the influence of transnational non-state actors. These complex relationships can be explored through both the liberal and realism lenses and can later explain the debate of power from complex interdependence.

The term "complex interdependence" was claimed by Raymond Leslie Buell in 1925 to describe the new ordering among economies, cultures, and races. The very concept was popularized through the work of Richard N. Cooper (1968). With the analytical construct of complex interdependence in their critique of political realism, Robert Keohane and Joseph Nye explore how international politics forever changed due to the emerging complex interactions and interdependence among states. The theorists recognized that the various and complex transnational connections and interdependencies between states and societies increased, while Military force and power balancing are decreasing but remain essential. In coining the interdependence concept, Keohane and Nye also notably differentiated between interdependence and dependence in analyzing the role of power in politics and the relations between international actors.

From the analysis, complex interdependence is characterized by three characteristics, involving

Thus, Keohane and Nye argue that the decline of military force as a policy tool and the increase in economic and other forms of interdependence should increase the probability of cooperation among states. The theorists' work surfaced in the 1970s to become a significant challenge to political realist theory in international politics. It became foundational to current theorists that it be categorized as liberalism (international relations), neoliberalism, and liberal institutionalism. Traditional critiques of liberalism often define alongside critiques of political realism. They both ignore the social nature of relations between states and the social fabric of international society. With the rise of neoliberal economics, debates, and the need to clarify international relations theory, Keohane has most recently described himself as merely an institutionalist. This theory's purpose is to develop sociological perspectives in contemporary International relations theory. Liberal, neoliberal, and liberal institutional theories continue to influence international politics and have become closely intertwined with political realism.

Multiple channels that are present in complex interdependence are "connect societies, including informal ties between governmental elites as well as formal foreign office arrangements." The second type is "informal ties among nongovernmental elites where contact usually happens either face-to-face or through telecommunication. The last type is "Transnational organization," including organizations such as multinational banks or corporations. A more straightforward way of thinking of these concepts is by condensing them by calling them interstate, transgovernmental and transnational relations. Therefore, these channels can be a way of communication for states and are a considerable part of complex interdependence.

Foreign affairs issues are becoming increasingly crucial regarding complex interdependence. Countries' policies are all interconnected, even if they are merely domestic. Though the policies may appear to address one countries' issues, any laws may have regional and global implications. These implications have encouraged consulting agreements among countries through liberal institutions like the IMF and the European Community. The presence of Anarchy allows for International Politics to align favorably with domestic issues and laws determined by developed, pluralistic domestic countries.

Force has always been emphasized in international politics based upon the idea that (1) states compete for power, and that (2) survival is a state's chief goal under anarchy (security dilemma). However, military power and the role it has played has diminished for a few reasons. The first reason is because a state's fear of being attacked has declined (especially among industrialized, liberal states), because of the current lack of incentive among other countries to invade, as well as mutually beneficial relationships and cooperation (due to complex interdependence). With 20th century goals such as environmental and economic welfare, force is ineffective. The second reason is that we now see force used more as a deterrent (for example, Nuclear weapon). Goals that do relate to a state's security will most likely not use force to be achieved, and if used, could have steep consequences. This, as well as the domestic opposition that follows, are added reasons why states are hesitant to use force. One concern that stems from the diminishing role of military force is that Terrorism may be used more frequently, since most states are less likely to commit troops overseas.

The use of force, according to the author, will depend upon how much a state is affected by actions transpiring elsewhere. For example, if effects on that state are little, the chances of that state using force are also little. It will also depend on whether or not the issue is one of life or death. In this case, the realist theory would prevail and the state could very well end up taking forceful action. The author concludes that in each situation, we must decide which is more applicable, complex interdependence or realism.