A Cross-Border Joint Venture Ecosystem (CBJV Ecosystem) is not just a single joint venture between two firms from different countries; it is a structured network of partners, institutions, assets, and governance mechanisms that collectively enable sustained cross-border value creation. The core conclusion of this article is simple: most cross-border JVs fail not because of strategy or market choice, but because firms treat the JV as a standalone entity rather than as part of an ecosystem that must be deliberately designed and governed. Key points include (1) why ecosystems, not contracts alone, determine performance, (2) how decision rights, incentives, and KPIs must be distributed across borders, and (3) why institutional differences are often more decisive than cultural ones. Readers gain a practical definition, a decision framework grounded in real cases, and a checklist they can immediately apply when evaluating or redesigning a cross-border JV. This article is written for executives, investors, and corporate planners who need clarity before committing capital, people, and reputation across borders.