The first Common Security and Defence Policy (CSDP) mission was launched in 2003. Since then the EU has launched 24 civilian missions and military operations. Despite the tendency of military operations to attract more attention, the majority of CSDP (Common Security and Defence Policy) interventions have been civilian missions. Since the beginning the actors involved in CSDP recognised the need to learn from the different aspects of missions and operations. The tools and methodologies to guarantee a successful learning process have evolved over time together with the evolution of CSDP. This study represents a first stock-taking exercise of the lessons learned processes at the EU level. The study is divided in three major components. The first component looks at the available literature on the subject of knowledge management with regard to CSDP missions and operations. The study then draws upon short case-studies from the 21 missions and operations to-date with a specific focus on the lessons identified and (possibly) learned in practice. The study concludes with a number of recommendations targeted at how the lessons learning processes could be improved including specific recommendations on the role of the European Parliament.