In this chapter, we outline a model of solution design for sustainability problems plaguing developing countries such as of falling agriculture productivity and inadequate sanitation. Solution design is a design-based approach that starts from the needs and concerns of real people with proactive attention to negative side effects. Solution design combines design thinking with social science in a stakeholder process. We illustrate the need for solution design for the cases of bollworm pest and the elimination of open defecation in India. The solution design approach merits attention from scholars of environmental economics because system change pathways not only require coalitions but also helpful policy frameworks that tilt the playing field in the right direction so that environmentally and socially advantageous change can take place in a sustained way. Experience with action research may also allow them to engage with the concrete and to offer a welfare analysis of particular solution designs (for example by costing negative effects alongside monetizing benefits). Attention to local needs and capabilities, aspects of (weak) governance and possible side effects of acclaimed solutions by environmental economists will improve the relevance of the analysis through a better treatment of innovation in a place-based manner and people/agency aspects of change.