Ship transport can be said to be the original Intelligent Transport System and developments in this sector should be of interest for ITS research in other modes. This paper will investigate the requirements to a Maritime ITS architecture and describe elements of a possible solution. A driving force behind this architecture is the international nature of ship transport and the need to establish standards for information exchanges to further increase efficiency, reduce greenhouse gas (GHG) emissions and improve the security in the sector. Obviously, reduction of GHG emissions through operational measures can also reduce costs. This has been realized by the shipping community and the e-Navigation (by International Maritime Organization - IMO) and e-Maritime (by European Union - EU) initiatives testify to this. Both initiatives have identified the information architecture as critical for the future development of the ship transport area. The development of a maritime ITS architecture needs to consider legacy systems, the international nature of shipping, international legislation and standards as well as highly varying quality of service on available communication channels.