Business model design in this work refers to the architecture of a firms boundary- spanning transactions with other business model participants. The study at hand addresses calls of prior research by developing and testing a theoretical model that integrates relationship marketing into the theory of business model design with respect to the requirements of entrepreneurial ventures in the early stage of the organizational life cycle. The analysis of large-scale survey data demonstrates that the entrepreneurial ventures performance of efficiency-centered business models increases with larger relationship marketing efforts (i.e., relationship-specific investments) towards a companys key customers. In contrast, the performance of novelty-centered business models increases with a lower degree of such marketing efforts