Gouy-Stodola Theorem as a variational principle for open systems. Umberto Lucia Dipartimento Energia, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy umberto.lucia@polito.it Abstract The recent researches in non equilibrium and far from equilibrium systems have been proved to be useful for their applications in differ- ent 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 fun- damental 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. 1 arXiv:1208.0177v1 [math-ph] 1 Aug 2012