Reconciling and operationalizing the three main concepts of sustainable development-the economic, ecological, and sociocultural-poses formidable problems. Environmental economics and valuation can play a key role in helping to incorporate concerns about biodiversity loss into the traditional decision-making framework. A case study from Madagascar examines the impact of a new national park on tropical forests by using both conventional and newer techniques to economically value damage to forests and watersheds, timber and nontimber forest products, other impacts on local inhabitants, impacts on biodiversity, and ecotourism benefits. In the Sri Lanka case study, an integrated energy-environmental analysis was developed, which helps to eliminate projects with unacceptable impacts, and redesign others. Where economic valuation of environmental impacts was not possible, multiple attribute evaluation techniques were used. Improving the incomes and welfare of local communities, especially poor ones, while simultaneously preserving physical and biological systems, offers opportunities for developing countries to pursue all three goals of sustainable development in a complementary manner.