Contemporary maritime security threats such as piracy, smuggling and illegal fishing are major concerns in Southeast Asia. responding to these threats have long been seen as the responsibility of governments. This article demonstrates how new actors have become involved in addressing national and regional maritime security threats in Southeast Asia. Focussing on three distinct types of new actors — for-profit actors, not-for-profit actors and multilateral institutions — the article provides an understanding of the (sometimes controversial) nature of their responses to threats and the relationships between these new actors and the state. By revealing the contribution made by new actors in Southeast Asia — a region where governments are particularly protective of their sovereignty — this article shows how and why established patterns of security governance in Southeast Asia are changing and offers new insights into alternative methods for tackling maritime security threats.