This thesis evaluates if there is already sufficient regulation to effectively prevent maritime terrorism or whether the current international law on maritime security needs to be improved to reduce the vulnerability of possible maritime targets. The legal question on the definition of maritime terrorism and how to distinguish maritime terrorism from piracy is discussed. Further the most important incidents of maritime terrorism that have happened in the past and today`s most feared scenarios of maritime terrorism are presented. The thesis explains how the legal regime on maritime security changed in the aftermath of 9/11. The main chapter of the thesis analysis the legal regime concerning the prevention of maritime terrorism by dealing with the most relevant “risk factors” of maritime security, i.e. the vessels, the ports, the containers, the crews and the passengers. With regard to the risk factor “vessels” the thesis first presents regulations on vessel security as such and then the legal situation concerning the boarding of vessels to prevent the supply of terrorism. Finally the author gives an own evaluation of the current legal regime and presents own suggestions on what should be improved.