The concept of non-traditional security opens up the possibility that someone besides the state is threatened, and someone or something besides another state is doing the threatening. Actions by maritime non-state actors designed to maximize their own security can lead to state security problems and even interstate conflict. Using three cases of maritime security issues in East Asi—territorial disputes, maritime piracy and terrorism—this chapter focuses on two broad scenarios in the maritime domain where state and non-state security may be at odds. Maritime disputes would seem to be the archetypal traditional security problem, and indeed they are: from a rationalist understanding of war, territorial disputes are exactly the kinds of focal points for disagreement where information problems about resolve and capability come to the fore. The main relationship between terrorism and the maritime domain is thus one where the social and economic networks that criss-cross the maritime domain support terrorist groups’ logistical activities.