This study explores why academic entrepreneurs seek patents for their inventions before and after spin-off creation. Specifically, we examine (1) the relative impact of academic, business, and entrepreneurial rationales and (2) changes in patent propensity throughout the founding process. Findings based on 160 technology spin-offs combined with patent data show that some academic and business rationales, but also entrepreneurial rationales (technological uncertainty, tacit knowledge) affect patent propensity. Surprisingly, academic entrepreneurs with patents prior to founding patented less after founding. We discuss the implications of our results both in terms of contribution to the current literature and technology transfer policies.