This monograph deals with the economic analysis and mathematical modeling of the diffusion of interorganizational information systems and networks. One result is that the models have to consider explicitly the various objectives and dependencies between system owner and system user. The proposed models are based on diffusion theory, network economy as well as on a methodical paradigm that closely relates to engineering sciences and has become known as «gray modeling». All models are first theoretically developed and subsequently exemplified by suited numerical examples. The results will help economists and system analysts to identify the success factors for the growth of network products and to propose concrete solutions for their introduction.