The rapid evolution of the global economy, driven by digitization and modularization, has outpaced existing theoretical tools. This paper proposes a unified analytical framework for understanding the complexity of digital industries through the lens of Massive Modular Ecosystems. To operationalize this concept, the paper develops a systematic methodology for mapping prevailing and alternative governance structures across interconnected, layered, and nested ecosystems. Synthesizing insights from the global value chain governance, modularity and standards, and business ecosystem literatures, the paper demonstrates how modular governance enables distributed innovation, while non-modular governance structures - including captive supply relationships, relational partnerships, and hierarchical control - support greater value capture and strategic control. The defining element of a Massive Modular Ecosystem is not that every relationship is purely modular, but that non-modular relationships operate in a "sea of modularity," a context where modularity prevails. Using a case study of the mobile phone industry, the paper depicts a Massive Modular Ecosystem characterized by a dynamic mix of internalization and outsourcing, with a few dominant players in each sub-ecosystem but no dominant actor overall. The study explores the broader implications of Massive Modular Ecosystems, including their impact on market structure, technological innovation, and global-scale economic geography. Increasing geographic specialization and clustering of sub-ecosystems create strong interdependencies across countries, making aggressive policy interventions risky and potentially leading to unintended consequences. Efforts to build self-sufficient domestic industries may be impractical and costly, while attempts to decouple from Massive Modular Ecosystems can lead to exclusion from critical innovation networks and standard-setting processes. By providing an integrative analytical tool, this paper offers policymakers, business leaders, and scholars a systematic approach to navigating the complexities of modern digital industries
