The __viable systems approach__ (__VSA__) is a systems theory in which the observed entities and their environment are interpreted through a systemic viewpoint, starting with the analysis of fundamental elements and finally considering more complex related systems (Ludwig von Bertalanffy, 1968).
The assumption is that each entity/system is related to other systems, placed at higher level of observation, called supra-systems, whose traits can be detected in their own subsystems (principle of system hierarchy) - wikipedia 
The fundamental unit of analysis is a system made up of many parts or structures (Talcott Parsons, 1971). In this sense, every entity (a firm, or simply an individual, a consumer, or a community) as a system can be considered a micro-environment, made up of a group of interlinked sub-components which aim towards a common goal (this is the condition, for the aggregate, to be qualified as a system).
The viable system model was first proposed by Stafford Beer. In general terms, a viable system is finalized toward its vitality throughout viable behavior based upon consonant and resonant relationships.
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