Isolationism is a political philosophy advocating a national foreign policy that opposes involvement in the political affairs, and especially the wars, of other countries. Thus, isolationism fundamentally advocates neutrality and opposes entanglement in military alliances and mutual defense pacts. In its purest form, isolationism opposes all commitments to foreign countries including treaties and trade agreements. This distinguishes isolationism from non-interventionism, which also advocates military neutrality but does not necessarily oppose international commitments and treaties in general.

This contrasts with philosophies such as colonialism, expansionism, and liberal internationalism.