NbS Triple Win Toolkit: Implementation Guidance – Executive Summary 7 Very few projects conducted or provided a cost effectiveness or financial analysis, though the literature provided several reviews of cost effectiveness for coastal or marine projects. The cost-effectiveness evaluations that were available were used to justify a project or to gain project approval. There is little evidence of the economic case for NbS being reassessed after the project hasbegun to assess whether assumptions were correct or whethercosts and benefits accrue as anticipated in the initial assessment. Post-project evaluation was infrequently conducted, especiallyfor marine and urban settings though marine was slightly more common than urban. This could be due to the reporting requirements of the programmes selected or limits to post-project funding for monitoring and evaluation. NbS are effective when a suite of interventions is used, or when incorporated with other approaches (e.g., grey infrastructureor specific poverty reduction policies). Most of the case studies utilised several NbS interventions in their project approach.Many also deployed complementary approaches to achievethe triple win – through data improvement and early warningsystem development or tying activities to local public health work. NbS is mostly financed by the public sector and with grant funding. This is because the public goods which NbS generate are often difficult to convert into financial returns for the private sector. The risks and uncertainties associated with both NbS interventions and investing in ODA context remain prohibitive in comparison with conventional investment opportunities. The review of case studies and key literature produced a set of underlying Principles (see Figure 2) which describe how an NbS project can contribute to a triple win in the context of ODA funding. Give parityto all three pillars of the triple win > Design with longevity and futureproofingin mind > Put in place social and environmental safeguards > Provide sustainable, equitable financial incentives > Build robust,long-term monitoringsystems > Engage local communities in a participatory approach > Account forsite-specific and complex dynamic contexts > Emphasisean adaptive management approach > Consider trade-offs and synergies across multiple scales > Principles Nine Principles for Nature-based Solutions. These principles are the product of the review and synthesis of core principles fromthe many interventions that qualify as NbS, other meta-analyses, and lessons learned from the case studies.