Suppliers have become resources for innovation and competitive advantages. To realize those potentials specific competencies have to be developed in a partnership between customer and supplier. The success of those development projects and also the effort that has to be put in depend on several factors. One of those factors is the motivation of the supplier organization. An empirical study shows that the motivation can be described sufficiently exactly by particular characteristics. Moreover particular influencing factors with significant impact on supplier motivation could be extracted. Those findings can be used to control supplier development projects better which in turn will lead to qualitatively better results and a better cost-benefit ratio.