Phase two of the Brexit negotiations is starting and all eyes are on the future economic partnership. The other key issue – the future security partnership – is often neglected. One reason for this neglect is that stakes are lower in this policy area that is far less integrated in the context of the EU. A second reason is that there seems to be more room for compromise. In fact, both Brussels and London have indicated that while basing post Brexit defence cooperation on existing models, they might strive for a more ambitious version. What does this mean in practice? This policy brief assesses two existing and two new models for defence cooperation in light of EU and UK interests.