Entrepreneurial ecosystems have quickly become one of the most popular topics in entrepreneurship research. Ecosystems are the characteristics and factors of a place that support high-growth entrepreneurship. This provides the ability for the field to provide important policy insights about how to aid the development of high growth, innovative ventures, as well as generate new insights into the relationship between the entrepreneurship phenomenon and the contexts it takes place within. However, work in the field remains undertheorized, with a little understanding of how the entrepreneur benefits from being in a strong ecosystem. This chapter argues that it is helpful to return to Ed Malecki’s work in a previous volume of this series, which explored the importance of networks. His work has contributed to a very broad stream of work on entrepreneurial environment. Using this as a starting point, this chapter distinguishes between “top-down” approaches to study ecosystems, which focus on the actors and factors that make up an ecosystem, and a “bottom-up” approach, which instead examines the ways in which entrepreneurs use their ecosystem to get the resources, knowledge, and support they need. The chapter concludes by suggesting how a research agenda for a bottom-up study of ecosystems can be informed by Malecki’s work.