Accelerator programs are an increasingly important part of entrepreneurial ecosystems. While accelerators have core defining features—fixed-term, cohort-based educational and mentorship programs for startups— there is also significant variation amongst them. In this paper, we relate key variation in the antecedents, organizational design and operation of these programs to theories of firm-level entrepreneurial performance. We then document descriptive correlations between these design elements and the performance of the startups that attend these programs. In doing so, we probe the connections between design and performance in ways that integrate previously disparate research on accelerators and expand our understanding of startup intermediaries. Our findings delineate the building blocks as well as an agenda for future researchers to build upon not only our understanding of accelerators, but also our understanding of what new ventures need to survive and flourish.