The 2009 Treaty of Lisbon introduced a concept known as the “Common Security and Defence Policy” to the legal structures of the European Union. While not initially envisioned as a military pact, the Treaty of Lisbon saw the expansion of the EU’s policy purview and laid the groundwork for the European Union to act as a unified power in foreign affairs. While the prospects for Ukrainian membership of NATO remain unclear, Kyiv’s EU candidacy means that certain elements of collective security may be secured through future membership of the European Union. This article will examine areas of security and defence integration between the European Union and Ukraine, and compare the concepts of collective security in NATO and the EU.