This article examines the rise of maritime security in concept and practice. We argue that developments in the maritime arena have flown beneath the radar of much mainstream international relations and security studies scholarship, and that a new agenda for maritime security studies is required. In this article we outline the contours of such an agenda, with the intention of providing orientation and direction for future research. Our discussion is structured into three main sections, each of which outlines a core dimension of the maritime security problem space. We begin with a discussion of the issues and themes that comprise the maritime security agenda, including how it has been theorized in security studies to date. Our argument is that the marine environment needs to be understood as part of an interlinked security complex, which also incorporates strong connections between land and sea. Second, we examine the ways in which maritime security actors have responded to these challenges in practice, focusing on issues of maritime domain awareness, coordination of action, and operations in the field. Third, we turn to the mechanisms through which the new maritime security agenda is being disseminated to local actors through a process of devolved security governance. We focus particularly on efforts to distribute knowledge and skills to local actors through capacity building and security sector reform. In the conclusion, we outline the future challenges for maritime security studies that follow from these observations.