Many organization theories consist of an interpretation frame and an idea about the ideal equilibrium state. This article explains how the equilibrium concept is used in four organization theories: the theories of Fayol, Mintzberg, Morgan, and Volberda. Equilibrium can be defined as balance, fit or requisite variety. Equilibrium is related to observables dependent on the definition of organization as work organization, formal organization or artifact organization. Equilibrium can be explicitly related to performance in the theory used, enabling cross-sectional research. The discussed theories can be mapped on a state space model in a way that clarifies the equilibrium concept, namely a mu-space (Fayol and Morgan), or a gamma-space (Mintzber...