Entrepreneurship research is increasingly taking into account external factors in order to provide context for the conditions under which new firms are created. Thus, the entrepreneur is increasingly recognized as a constituent part of the ecosystems in which they operate. In addition, a strong and vibrant ecosystem should be host to diversity—the presence of migrant entrepreneurs is a sign of this diversity, contributing to the ecosystem at the city level. This chapter focusses on a particular group of entrepreneurs, Polish migrant entrepreneurs based in the city of Glasgow, UK, and provides details of exploratory research that examines the influence of the entrepreneurial ecosystem on their new venture creation process. In order to examine which external factors are of importance developing vibrant ecosystems, and to draw attention to the role of proximities in facilitating their use by Polish migrant entrepreneurs, this chapter synthesizes the current entrepreneurial ecosystem literature with that discussing opportunity structure and proximity. The results suggest that both geographic and cultural proximity are important factors in accessing market and resources within the local migrant community. However, it also appears that despite positive effects in the start-up phase, the high level of proximity displayed between entrepreneurs and their market base can constrain future business growth potential—leading to a lack of diversity and suggesting a lack of local diversity within the community based sub-ecosystem.