Maritime security is affected by global trends in security-related issues, but also retains unique characteristics related to the maritime domain. Over the past thirty years, several trends in security policy have led to an increasingly visible role for non-state actors in supporting maritime security. Existing research on the ways that non-state actors such as civil society organizations and private-sector entities contribute to security is reviewed. Their roles as advocates, service providers, and (in limited ways) providers of direct security services are explored, and an analysis of counter-piracy activities in the early twenty-first century is used to assess the relevance of this existing research for the maritime sector. A strong counter-piracy role is identified for non-state actors in the maritime sector, potentially greater than the role they play in land-based domains.