This chapter examines sub-systemic actor’s duties. It treats NATO as indicative of a collective defence organization and the European Union (before the Lisbon treaty that contains two collective defence clauses) as indicative of a collective security organization. This chapter argues that NATO has, if requested to help by a member country, a contractual (Article 5) – and thus overriding – duty to protect a member state, and when must cause is satisfied, with securitization. It is argued that Article 5 is now somewhat outdated and that – going forward – just reason (i.e., the existence of an objective existential threat) + macro-proportionality, and not armed attack, should be the threshold for collective political action. The obligation to use securitizing measures, however, rests with the satisfaction of must cause. This chapter also argues that in collective security organizations, the obligation to securitize insiders, rests with remedial responsibility triggered by ties of community/friendship, this means that unlike in collective defence organizations, the obligation to securitize insiders can be overridden.