Publisher Summary This chapter presents a brief review of an operability approach—that is, based on some simple geometric concepts utilized to examine the steady state and dynamical characteristics of a given plant in the design stage. The steady-state operability framework uses the steady-state model of the process and aims to calculate whether the input ranges are sufficient to achieve the desired output ranges in the presence of the expected disturbances. A steady-state operability index is thus defined. The steady-state operability characteristics are quantified by comparing two spaces related to the inputs or the outputs of the process. With respect to the input variables, one can compare the available input space versus the desired input space. Steady state operability is a necessary but not sufficient requirement for a well-designed plant, as the dynamic characteristics should also be considered.