Movement and international trade of goods is largely done by sea and depends on maritime routes, placing great importance on security in public ports, harbours and other maritime facilities. Principal sources of danger to maritime transport and seaports include terrorism, human trafficking, organized crime and eco-terrorism. Terrorism - one of the most prominent threats - is the calculated use of unlawful violence with the intention of creating generalized pervasive fear for the purpose of attaining religious, ideological or political goals, with the main terrorist targets within the maritime sector being: seaports, ships, bridges, oil and gas platforms. These threats pose significant danger to the safety of people, property and the environment, making it necessary to implement effective protection measures in seaports, develop security procedures and protocols and issue suitable guidelines for assessing and combating identified threats. One of essential international regulations for enhancing the security of ships and port facilities is the International Ship and Port Facility Security Code (ISPS) in force since 2002. Republic of Croatia adopted the national Act on Maritime Ship and Port Security for the same purpose. Aim of such ordinances and legislation is to establish procedures and protection measures for handling specific security threats or harmful events, i.e. procedures used to prevent possible incidents and accidents. Given that maritime security is of paramount importance to the world economy, ecology, as well as national economies, various security-related confederations, professional guilds and private security companies are being established, supported by numerous laws, regulations and codes regulating the security of seaports and ships. Confederation of European Security Services (CoESS), Croatian Security Association and private security companies, along with relevant state institutions and bodies, are focused on solving maritime and port security issues and developing qualified personnel and technologies. The goal of this paper is to explore basic concepts of port security and understand how it is attained, review roles and features of security segments within the port, thoroughly examine the state of security in ports around the world and in Croatia and how it is implemented in real-situations. Special emphasis was placed on studying the role of private security actors in the governance of port security.