The concept of Natural Capital facilitates the re-introduction of natural constraints in the analysis of economic development. This allows us to bring the notion that nature is a limited asset that provides essential services for human well-being and survival. This is important to reincorporate Nature’s limitations into the standard framework of economics, the discipline studying and providing advice on how to address scarcity. One step in this process is to put values on the services provided by Nature, something relatively straightforward for those materials, from water to minerals, providing marketable inputs for production processes, but far more challenging for those that are non-marketable but play a critical role in maintaining the integrity of ecosystems. When thinking about natural resources, Economic Theory should incorporate their heterogeneity and limited availability, so many of the standard assumptions must be revised and models must be adapted to deal with issues such as rents and declining productivity. Related issues such as the substitutability of natural and produced capital, and the related concept of weak sustainability are also addressed in this chapter. Methodological challenges to measure and set values to natural capital are also discussed here.