Significant reductions in anthropogenic emissions and increases in CO2 sinks are needed to meet the 1.5 centigrades threshold for global warming set out in the Paris Agreement and reach the climate-neutrality goal of the European Green Deal by 2050. The CO2 sink provided by forests, including old-growth forests, partially offsets the rise in anthropogenic CO2 emissions, providing a large-scale buffer to climate change. Depending on their characteristics and local circumstances, such as management practices or ecosystem services, forests may range from net CO2 sinks to sources. The project 'OPTimising FORest management decisions for a low-carbon, climate resilient future in Europe (OptFor-EU)' will build a Decision Support System (DSS) to provide forest managers and other relevant stakeholders with tailored options for optimising decarbonisation and other Forest Ecosystem Services (FES) across Europe. Based on exploitation of existing data sources, use of novel Essential Forest Mitigation Indicators and relationships between climate drivers, forest responses and ecosystem services, OptFor-EU has five specific objectives: (1) Provide an improved characterisation of the Forest-Climate Nexus and FES; (2) Utilise end-user focused process modelling; (3) Empower forest end-users to make informed decisions to enhance forest resilience and decarbonisation; (4) Provide a novel DSS service; and (5) Bridging different EU strategic priorities, robust science, and stakeholders in the forest and forest-based sectors. Based on a supply-demand approach, the methodology combines an iterative process of data consolidation, modelling, and co-development of solutions alongside forest managers and other practice stakeholders in all European Forest Types. The DSS will be designed and tested at 8 case study areas, to provide a ready-to-use service, near to operational (TRL7) at European level, while a user adoption and up-take plan will maximise the societal and business impact.