When they lack resources to commercialize science, entrepreneurs rely on intermediary organizations often within their local ecosystems. This paper seeks to improve our understanding of how intermediaries operate to advance the commercialization of science by providing a set of specialized services. We review five intermediaries commonly mentioned in the ecosystem literature: university technology transfer and licensing offices; physical space (incubators, accelerators, and co-working spaces); professional services providers; networking, connecting, and assisting organizations; and finance providers (including venture capital, angel investors, public financing, and crowdfunding). Specifically, we explore how these various intermediaries function and provide complementary and related services in support of scientific commercialization through entrepreneurship. After defining intermediation, we review the literature on each organization type, providing a definition and considering the contribution of the intermediary and the related policy implications. Each section concludes with suggestions for additional research.