Decision Support Systems (DSS) are supporting tools enhancing a decision-making process. Decision-makers are faced with the difficulty of taking decisions especially on very complex issues. This usually needs input of large data sets and a timely decision process is required. DSSs are multi-faceted tools to provide decision makers with an instrument to (a) reduce uncertainties, (b) simplify and speed-up the decision process without losing essential information, (c) avoid subjectivism induced by the decision-maker and (d) guarantee transparency of the entire decision process. The DSS approach was introduced in Ballast Water Management (BWM) because of the selective BWM approach, which means that the appropriate BWM measures to take vary depending on the different levels of risk posed by the intended ballast water discharge, which also depends on the BWM feasibility in certain circumstances. More precisely, it was soon recognised that a supporting tool is needed to provide transparency and consistency on BWM requirement decisions with the aim to improve environmental protection and to lessen the BWM burden on vessels.