Indicators for hazardous substances and biodiversity are to be developed to support regular assessments of whether HELCOMs strategic goals and ecological objectives have been reached, and whether implementation of the Baltic Sea Action Plan has been successful. The indicators should be fully in line with good ecological status (GES) as defined in the EU Marine Strategy Framework Directive, and the ensuing guidelines or criteria. The project will ensure the necessary cooperation and coordination, and the marine region-wide harmonisation needed to set Baltic Sea-specific targets for GES related to hazardous substances and biodiversity. Achievements: The HELCOM CORESET I project was set up to meet the need for a Baltic-wide, coherent assessment of the state of the marine environment. The selection of core indicators was a process guided by predefined principles, e.g. the indicators will be monitored by all Contracting Parties; cover the entire convention area; reflect or directly measure anthropogenic pressures; enable assessments under the BSAP and the EU MSFD. The CORESET expert group on hazardous substances developed 13 core indicators for concentrations of hazardous substances and their biological effects. Nine of the core indicators are based on concentration measurements and four on biological effects. All of the core indicators have quantitative targets, which give the status mainly in biota but in some cases also in sediment or water. Descriptions of the indicators are published in two interim reports and a final report.