国际关系现实主义是一组国际关系理论与实践，这一组理论强调权力关系对于国家行为的影响，关注民族国家之间的权力平衡以及对国家利益的追求。这一理论主张，国家在决策时权力与利益的考量高于理想或道德。与之相对的是「理想主义」。 根据独立变项的层次来区分，有结构现实主义（独立变项为体系层次）、古典现实主义（个人层次与国家层次）、新古典现实主义（体系与国家和个人层次都考量）

Realism is the predominant school of thought in international relations theory, theoretically formalising the realpolitik statesmanship of early modern Europe. Although a highly diverse body of thought, it can be thought of as unified by the belief that world politics is, in the final analysis, always and necessarily a field of conflict among actors pursuing power. Crudely, realists are of three kinds in what they take the source of ineliminable conflict to be. Classical realists believe that it follows from human nature, neorealists focus upon the structure of the anarchic state system, and neoclassical realists believe that it is a result of a combination of the two and certain domestic variables. Realists also disagree about what kind of action states ought to take to navigate world politics, dividing between (although most realists fall outside the two groups) defensive realism and offensive realism. Realists have also claimed that a realist tradition of thought is evident within the history of political thought all the way back to antiquity, including Thucydides, Thomas Hobbes and Niccolò Machiavelli.