METHODOLOGY: We started with the 400 fastest-growing metro areas ranked by Milken Institute’s Best-Performing Cities 2021 Foundations for Growth and Recovery. We considered each area’s ranking on the list of the Kauffman Foundation Index of Growth in Entrepreneurship, Metropolitan Area and City Trends, which examined the rate of startup growth, the share of scaleups, the high-growth company density and the density of venture-capital backed business exits.Many other lists that rank ecosystems, such as those examining venture capital to startups, only look at the largest cities in the United States. To capture the possibility of local venture capital investment that could flow to smaller cities, we looked at state-level data from PriceWaterhouse Coopers MoneyTree survey, which ranked level of venture capital investment in Q4 2020. PWC only uses large deals, but statewide rankings offer some insight into how much capital is available in that state. We used each state’s ranking on the Heartland Forward Most Dynamic Metropolitan Index, which considers performance-based metrics such as GDP and job growth, but notably it takes into account the proportion of total jobs at young firms and the educational attainment of potential employees. We also used the 2019 ranking of states’ business tax environments by the Tax Foundation. Cities in the Milken Institute report were rank-ordered in each category according to their ranking in the individual lists. The rankings were then assigned a point value. We weighted each of these five criteria equally. When several cities in one state were close to each other in the rankings and in geography, we combined them into a single ecosystem. When a city was missing in a ranking we weighted the average of the overall score in that column. In cases where ecosystems have a significant media buzz, we gave them a bonus score, which moved the following ecosystems up in the rankings: Denver – Aurora- Fort Collins – Boulder, Indianapolis, Houston-Sugar Land-Baytown, Washington, D. C., Miami – Punta Gorda, Salt Lake City – Provo – Orem.