This book deals with what are usually called SMEs (Small and Medium-sized Enterprises, including very small enterprises). But it begins by asking the question of the relevance, from an economic point of view, of this statistical category, defined, for example, as firms with fewer than 500 employees by INSEE1. The purpose of this paper is to provide an analytical framework for understanding this form of organization for the production of wealth, with a view to building actions to transform existing situations in order to increase the economic and social efficiency, not only of the enterprise but also of the territories in which it is located.