In international relations, the liberal international order describes a set of global, rule-based, structured relationships based on political liberalism, economic liberalism and liberal internationalism since the late 1940s. More specifically, it entails international cooperation through multilateral institutions (like the United Nations, World Trade Organization and International Monetary Fund) and is constituted by human equality (freedom, rule of law and human rights), open markets, security cooperation, promotion of liberal democracy, and monetary cooperation. The order was established in the aftermath of World War II, led in large part by the United States.

The nature of the liberal international order (LIO), as well as its very existence, has been debated by scholars. The LIO has been credited with expanding free trade, increasing capital mobility, spreading democracy, promoting human rights, and collectively defending the West from the Soviet Union. The LIO facilitated unprecedented cooperation among the states of North America, Western Europe and Japan. Over time, the LIO facilitated the spread of economic liberalism to the rest of the world, as well as helped consolidate democracy in formerly fascist or communist countries.

Origins of the LIO have commonly been identified as the 1940s, usually starting in 1945, with some scholars pointing to earlier agreements between the WWII-era Allies such as the Atlantic Charter in 1941. John Mearsheimer has dissented with this view, arguing that the LIO only arose after the end of the Cold War. Core founding members of the LIO include the states of North America, Western Europe and Japan; these states form a security community. The characteristics of the LIO have varied over time. Some scholars refer to a Cold War variation of the LIO largely limited to the West, and a post-Cold War variation having a more widespread scope and giving international institutions more powers.

Aspects of the LIO are challenged internally within liberal states by populism, protectionism and nativism. Scholars have argued that embedded liberalism (or the logics inherent in the Double Movement) are key to maintaining public support for the planks of the LIO; some scholars have raised questions whether aspects of embedded liberalism have been undermined, thus leading to a backlash against the LIO.

Externally, the LIO is challenged by authoritarian states, illiberal states, and states that are discontented with their roles in world politics. China, Russia, Iran and North Korea have been characterized as prominent challengers to the LIO. Some scholars have argued that the LIO contains self-undermining aspects that could trigger backlash or collapse.