This chapter discusses the conceptual framework underlying many approaches to sustainability. It explores how the concepts of natural limits, the importance of cultural diversity and biodiversity, and ecosystems’ durability or fragility have affected specific local environment—society dynamics and the work of sustainable development projects. The chapter introduces three core narratives that derive originally from environmental science: balance; limits; and diversity. The idea that nature is characterized by balance, or stabilizing relationships, is central within environmental sciences, especially ecology. The second concept, limits, is closely linked to “carrying capacity,” or the idea that a given ecosystem can provide a finite amount of food and other necessary resources. Sustainability has further been linked to the idea of diversity. Within ecology, diversity has to do with the number of species present within a community as well as the relative abundance of each species. The chapter also presents an overview of the key concepts discussed this book.