A key task in the ESMERALDA project dealt with identifying appropriate case studies to test the 'flexible methodology' in its different stages of development. Case studies consist of working examples in which mapping and assessment of ecosystem services were applied to address specific decision-making problems. Testing is understood as an iterative process of co-learning that involves project partners and stakeholders, enabling the refinement of the 'flexible methodology' and the development of guidelines to support its application. Testing is conducted through a series of workshops in different European contexts, each addressing a different set of themes and regions.<br> This paper illustrates the selection of case studies for testing the ESMERALDA 'flexible methodology' in its different stages of development. Particularly, case studies had to be selected in such a way that they are representative of: (i) the variety of existing conditions across the EU, in terms of data availability, spatial scale, levels of implementation of EU 2020 targets and expertise and experience in ES mapping and assessment; (ii) the geographical regions and biomes of the entire EU, including marine areas and the outermost regions; (iii) the variety of cross-EU themes relevant for ecosystem services, such as the Common Agricultural Policy, Green Infrastructure, Natura 2000 network, forestry strategy, water policy, energy, business and industry sectors and health; (iv) the variety of policy and planning processes that can be used to mainstream ecosystem services in real-life decisions, such as spatial and land use planning, water resource management, flooding under the EU climate adaptation action, energy policy, strategic environmental assessment, protected area planning.
