The article examines the formation of the Common Security and Defence Policy of the European Union and the first stage of its development (1999–2016). The legislative framework for European integration in security and defence is analyzed, primarily a number of treaties adopted at the end of the 20th and the beginning of the 21st centuries. It was found that their normative provisions began to be implemented within the framework of the EU CSDP (until 2009 – ECSDP), which was launched in 1999 thanks to the decision of the European Council. The key directions of the EU CSDP at the first stage of its development (1999–2016) were the implementation of peacekeeping operations, the formation of battlegroups, as well as the initiation of joint projects in the field of defence within the framework of the European Defence Agency. It was concluded that the first two directions carried out at the expense of the capabilities already available in each country, developed most dynamically. From 2003 till 2016, the EU carried out more than 30 peacekeeping operations in different parts of the world, and since 2005, multinational combat groups began to go on duty. However, the effectiveness of the implementation of the CSDP was affected by the lack of a single strategic culture among the participating countries, which led to cases of blocking proposals for peacekeeping operations or the use of EU battlegroups to resolve crises. A serious problem at the first stage was also the lack of joint financing mechanisms for peacekeeping operations and battlegroups, due to which most of their costs were transferred directly to the participating countries. It was revealed that the weakest link during 1999–2016 was the third direction of the CSDP, which related to the joint development of defence capabilities at all stages. The article concludes that the experience of the first stage of the CSDP was taken into account in the further reform of the EU, in particular, in the process of launching new initiatives during 2017–2022, which brought European defence integration to a new level. It is emphasized that Russia’s invasion of Ukraine proved the need for further reform of the CSDP while simultaneously strengthening the EU’s cooperation with the USA, NATO, and Ukraine.
