  The recent researches in non equilibrium and far from equilibrium systems
have been proved to be useful for their applications in different disciplines
and many subjects. A general principle to approach all these phenomena with a
unique method of analysis is required in science and engineering: a variational
principle would have this fundamental role. Here, the Gouy-Stodola theorem is
proposed to be this general variational principle, both proving that it
satisfies the above requirements and relating it to a statistical results on
entropy production.
