Deliverable report D2.2 of the EU Horizon 2020 Project OPTAIN (Grant agreement No. 862756). List of tailored and case-specific performance indicators (environmental and socio-economical) that help to evaluate the effectiveness of NSWRM monitored (existing measures) and modelled (potential future measures) in the OPTAIN case studies as well as used to establish a common language across project members and activities and to facilitate the knowledge sharing with stakeholders and the wider dissemination of project results. Summary: The content of this deliverable addresses the activities of the task 2.2 “Identification of performance indicators for the selected NSWRM” within the H2020 project OPTAIN. The core purpose of the task is to develop a customized set of indicators that allow assessing the effectiveness of selected (either existing or potential future) Natural/Small Water Retention Measures (NSWRMs) in and across the OPTAIN case studies (CS). The relevance of specific NSWRMs to face local challenges, their multifunctional nature and the manifold impacts they may have in the territory require identifying key elements that easily resume such features, while being flexible and adaptable enough to be used in different contexts. Therefore, task 2.2 elaborated a pathway to produce a list of Performance Indicators (PI), to set the focus for model parametrisation at different scales as well as to ensure an appropriate model setup and utilisation of modelling outcomes (WP4, WP5). For this reason, the screening, selection and tailoring of the most relevant indicators, to be used as PI, have been conducted from both the environmental (EPIs) and socio-economic (SPIs) points of view. The selection process was built at the interface between science and society, in a fruitful process of knowledge co-creation and sharing. As such, agreed lists of indicators can be used to support the harmonized approach of OPTAIN by establishing a common language across project members and activities, favour the understanding and the comparison of modelling results across CS, facilitating the dialogue with stakeholders and the wider dissemination of project results. The methodology followed to outline the customized list of indicators, to be used as PIs, was based upon the initial contribution of scientific / academic partners’ expertise to compile all the potential or candidate indicators and preselect the most relevant ones for the selected NSWRMs. As a result, we ended up with short lists of both environmental (25) and socio-economic (17) indicators that cover the most relevant issues of the OPTAIN case studies. In the second instance a participative approach involved local research teams and stakeholders in the valuation, adjustment and prioritisation of the most important indicators, also owing to the intensive consultation with OPTAINs Multi-Actor-Reference Groups (MARG). Based on the feedback obtained, the task 2.2 partners conducted an analysis of the commonalities and differences between CSs and scales. This allowed drawing the conclusion that, despite CS are experiencing diverse challenges, the most important issues covered by the selected indicators, and priorities given are very similar. Finally, for comparison purposes across CSs, a common set of PIs is proposed, including first discussions on the best way to represent selected PIs based on monitoring and/or modelling results to be available in CS.