A novel framework for distributed control and optimization of complex networks is introduced in this paper. Conservation laws for extensive quantities and the second law of thermodynamics lead to conditions for stability and optimality of the network. Interconnections between network nodes are represented through connectivity matrices and network graphs. A generalized version of Tellegen's theorem from electrical circuit theory plays a central role in deriving the objective function of the regarded dynamic process networks. The application of irreversible thermodynamics lead to stability and optimality results based on the co-content and content of the regarded process networks. The principle is illustrated in a pipeflow example.