This entry looks at the definition and characteristics of institutional ecosystems in the social and solidarity economy. After establishing the difference between a natural and a cultural ecosystem, we explore their specificities by indicating how and why they differ from the ecosystem of private enterprise. This leads us to situate the different logics involved with the construction of these ecosystems by presenting their components, their territorial logics of action, and the support methods deployed by the State which advance their development. Examples of initiatives are discussed throughout this summary in order to illustrate the diversity and plurality of the logics of action deployed by social and solidarity economy actors to fully achieve the goals they pursue. Through this, the summary focuses on the complementary aims shared between an offer of services which can be adapted to the needs of the populations, and the will to transform the institutional arrangements and the social relationships in place in a perspective of social and ecological transition.