Decisions related to the sustainable development involve the following: ?what to sustain? and ?how to sustain?. In general, these decisions are based on assumptions about the permanence of certain characteristics of the systems involved, be them natural or socio-economic. Moreover, these decisions can be only of ethical character or may involve formulations that include mechanisms for effective control, and search to steer the whole system towards a sustainable regime. The formal frameworks and the lines of thought employed in this process generaly relay in the maintenance of natural resources stocks and other factors. They do not consider, however, variations in technological production processes and social preferences. They do not, as well, take into account the spontaneous variability in the structure and components of the natural systems involved.This work aims an analysis of some existing concepts of Sustainability. It looks foward towards a stronger integration between the mathematical models and structuresin Sustainability studies, in particular while they relate to the interaction between the ecological, social and production areas.An investigation of Sustainability integrating all these areas has not yet been made, not only due to a lack of perception of variabilities about man-nature systems,but also because their models and representations have diverse nature. The evolution of ecosystems, for instance, is represented as dynamical systems, while theinteractions between people or organizations are represented as games and iterations in the productive system always appear as problems of control and allocation. When expressed in mathematical terms, these descriptions confine themselves to areas ofmathematics that are not easily integrated and which techniques do not keep, at themoment, a narrower relation.We propose, in this work, the language of general system theory as a means to represent the mutual interactions and influences between the natural, productive andsocial systems. We search also for a more integrated form to describe mathematically problems in these areas. This allows, at least, for a clearer perception of what ?tosustain? and of the interaction between components and processes in the mutable cases. This, in turn, provides a better stand about how ?to sustain?.