Russia’s full-scale invasion of Ukraine in 2022 has changed the security policy situation in the world. The EU and NATO are two security policy actors that, because of the situation in Ukraine, have received increased attention. Previous studies have discussed future scenarios regarding the two organizations and, among other things, whether the EU will take over NATO’s role as the primary security policy actor in Europe. The purpose of this essay is thus to highlight and compare the EU’s and NATO’s security policy ideas. This study is an idea analysis based on two theories in international relations, liberalism and realism, with the intention of examine whether the EU’s and NATO’s respective security policy ideas show any development since the end of the 90s, as well as classifying these as either liberal or realist theory. The essay also discusses ideological similarities and differences made visible in the organizations’ respective documents. The essay is based on an analysis of the EU’s Security Strategy (2003), the EU’s Global Strategy (2016) and the EU’s Strategic Compass (2022) as well as NATO’s sixth, seventh and eight strategic concepts (1999, 2010, 2022). The conclusion indicates that the EU’s and NATO’s security policy ideas include aspects that derive from both realism and liberalism, but that the EU emphasizes more ideas of liberalism while NATO’s ideas can relate better to realism. However, the EU has shown the most significant development, as the organization has approached the ideas of realism for its security policy by increasing the focus on defence issues and its military capacity.