Unregulated or lesser regulated maritime spaces are ideal theatres of operation and mediums of transportation for terrorists, insurgents and pirates. For more than a decade, the Indian Ocean waters adjoining Somalia have been a particular locus of such activities, with pirates hijacking vessels, and Al Qaeda and Al Shabab elements travelling between Africa and the Arabian Peninsula, operating lucrative businesses and even staging deadly operations at sea. However, these operations and threats remain, by and large, understudied. Responses to the two threats have varied, highlighting the lack of cohesive regional and global institutions with the mandate and the capacity to address them. Those scholarly deliberations on Indian Ocean maritime security focus on piracy and armed robbery at sea, while their terrorist/insurgent counterparts have eluded sustained scrutiny. This volume will help close that gap by looking at both from the field in Somalia and Yemen, within broader frameworks of regional maritime security and port-state control, international maritime law and the ongoing search for maritime resources. The European, African and Middle Eastern case studies add salience to the regional and international complexity surrounding maritime security off the Horn of Africa. This book was originally published as a special issue of the Journal of the Indian Ocean Region.