This technical report by Dstream Group examines Frankfurt am Main, Germany, as the world's foremost Digital Capital, detailing its evolution and the factors contributing to its global leadership in digital infrastructure. The report defines the concept of a Digital Capital and benchmarks the top ten cities worldwide, highlighting the critical role of Internet Exchanges, data centers, and connectivity infrastructure in establishing a thriving digital economy. It outlines the historical development of Frankfurt's Internet Exchange, DE-CIX, which has become a pivotal player in global interconnection. The analysis includes a ranking of the top ten Digital Capitals, with Frankfurt leading in several infrastructure categories. The report also discusses the economic impact of DE-CIX on the State of Hesse and Germany, emphasizing the interdependence between the city and its Internet Exchange. Furthermore, it addresses the future of digital applications and the need for innovative infrastructure to support the evolving digital landscape.