Entrepreneurial Ecosystem Mechanisms structures and synthesizes the field of entrepreneurial ecosystem studies with a focus on the empirical evidence of the underlying causal mechanisms. First the authors define some key academic 'tools' underpinning the analysis: concept, framework, model, theory, and mechanisms. Next, they identify, categorize, and organize the factors deemed most relevant to understanding entrepreneurial ecosystems: a framework. This framework provides the foundations for a model where the specific functional relationships among particular variables or indicators are hypothesized to operate in some well-defined set of conditions. Five causal mechanisms are conceptualized that are grounded in earlier work including (1) interdependencies between ecosystem elements, (2) the link between entrepreneurial ecosystems and entrepreneurial outputs, (3) wider socio-economic development, (4) downward causation, and (5) links and flows of ideas, people, and resources between different entrepreneurial ecosystems. This systematic literature review synthesizes empirical studies on the causal relationships among the ecosystem elements and how they are linked to outputs and outcomes. The goal is to develop a comprehensive and mechanism-based understanding of the entrepreneurial ecosystem concept, how it can contribute to entrepreneurship and economic development policy, and our wider understanding of the contextual nature of entrepreneurship. While recent reviews of the entrepreneurial ecosystem literature have sought to bring together this rapidly shifting field, this monograph adds to these works in two key ways - first, by embracing a broad literature covering the entirety of the entrepreneurial ecosystem concept rather than specialties such as ecosystems in emerging economies or specific domains, and second, by drawing on this literature to identify the empirical evidence for the five casual mechanisms linking the contexts in which entrepreneurship takes place with specific outcomes such as firm growth, innovation, and increases in overall welfare. The authors discuss the implications of the results in light of existing research agendas as opposed to developing a new one with the aim of the review to synthesize existing work. This is crucial for the credibility of the entrepreneurial ecosystem concept and its future within academic research and policy and business practice more broadly.