Ecologists deem the alterations caused to biological diversity by the transfer and spread of alien (non-indigenous) invasive species to be one of the most serious threats to biodiversity - second in impact after habitat destruction. With the exponential growth of global trade, facilitated by maritime traffic, the spread of alien species has grown accordingly. Although maritime transport is not the sole source of the invasion, it is the major source. Unlike with the ‘traditional’ forms of marine pollution, the transfer of marine organisms is virtually irreversible, and the consequences may be permanent. Three main vessels-source vectors for the transfer of organisms have persisted: ballast water (including sediment), hull fouling, and the cargo itself. This study focuses on ballast water - in itself important for the stability and safety of the ship and thus a key component of (global) maritime traffic. First, some key features of the 2004 IMO Ballast Water Convention are briefly discussed. Thereafter, an overview of ballast-water management stand¬ards under the Convention is provided. In particular certain basic elements, particularly those relevant for the enclosed or semi-enclosed sea areas, are analysed. Finally, in view of the particular situation of some enclosed or semi-enclosed seas, aspects of measures adjusted to respond to their special needs are examined.