The European security environment is currently significantly affected by Russian aggression against Ukraine. However, right from the start of the war, the European Union and its member states acted decisively, they unequivocally condemned the Russian invasion of Ukraine and began to help it politically, economically, humanitarianly and by supplying military equipment, weapons, ammunition, and training members of the Ukrainian armed forces. And although no European member state of the European Union or the North Atlantic Alliance has been attacked, the ongoing conflict negatively affects European stability and disrupts the European security and defence system. That is also why the authors, using relevant scientific methods and approaches within the framework of interdisciplinary research, deal in the article with some selected aspects of European security and defence in the context of the conflict in Ukraine. They point out how Russian aggression has influenced discussions about the roles of the European Union in ensuring security and defence on the European continent, shed light on the Union's security and defence policy, deal with issues of European strategic autonomy and related relations between the EU and NATO, and at the end of the article indicate challenges, which are closely related to European security and defence in the context of the war in Ukraine.