In the face of the ever growing concern about the alterations that human activity produces in the environment that supports it, emphasis begins to be placed on the application of sustainability criteria, including in the process of territorial and urban planning.

If what is sought is the conversion to sustainable models, the importance of understanding what sustainability is becomes obvious. Once the concept is understood, it is basic to determine what aspects define a system so that it may be considered to be sustainable and, reciprocally, to reveal what systems may not be considered to be such: in these cases, the causes will identify the pathology to be corrected, and the effects the impacts to be eliminated. This thesis defines those general aspects; the focus is on its concrete application to the sphere of planning and to defining contents and techniques in order to develop planning based on these concepts.

Among the conclusions thereof, it is seen that sustainability is a single possible vital process that makes the existence of living beings possible, in particular, man's existence, and their perpetuation on the planet. This is only effective as a comprehensive procedure and not as the sum of initiatives developed independently from one another. The conversion to sustainability is urgent for all the components of the global system represented by the Earth, and urban planning is one of those components, so that traditional planning formulas that overlook studies on environmental equilibrium should not be admissible. The change toward sustainable planning begins by accepting that this forms a part of an overall system, and ends up by defining modes of life integrated into the environment that supports them.