Social identities shape founders’ social motivation, self-evaluation, and frame of reference. However, little is known about how founder social identities shape new ventures’ business model designs. This study addresses this gap by arguing and empirically testing how and why founders with different social identities systematically design different business models. Specifically, we argue that Darwinian founders design efficiency-oriented business models, Communitarians design consumer-oriented business models, and Missionaries design sustainable-oriented business models. We also establish important boundary conditions of these relationships, particularly the core founder. We will test our predictions in a sample of 1‘019 new ventures from the German-speaking part of Europe. We contribute by establishing founder social identity as an important antecedent of business model designs and by linking founder social identities to firm strategy.