A distinct branch of socio-environmental research, grounded in the physical principles of conservation of mass and energy, applies a systems modeling approach to society–environment interactions, emphasizing material and energy flows. Technology and technological advancement, alongside population and resources, feature prominently in determining the metabolisms linking society and nature. This approach mostly focuses on analyzing industrial systems (e.g. Ayers and Kneese, Meadows et al., Beck, Graedel et al.) but also offers insight on agrarian societies (Boserup) and hunter-gatherer communities (Fischer–Kowalski). Across these levels of social organization, technology is variously viewed as overcoming the limits nature places on society, as facilitating the resource exploitation and production of waste that lead to social collapse, or as the basis for internalizing externalities and building a circular economy. Key readings constituting this branch of socio-environmental research draw on tools from economics and engineering, such as input–output models, system models, feedback loops, environmental impact analysis, and material and energy flow accounting.