Since the adoption of the International Convention for the Control and Management of Ships' Ballast Water and Sediments by the International Maritime Organization in 2004, rapid progress has been made in the ballast water treatment technologies necessary to deal with the problem of the migration and spread of aquatic species. Although there was some doubt at the time of the Convention's adoption regarding the development of treatment technologies, thanks to the intelligence and efforts of those involved they will soon be ready for use. This paper will introduce the current state of the ballast water treatment technologies, which play a leading role in the adoption of the convention and in providing a solution to the ballast water problem.