The vision of a seamless, patient-centric digital health ecosystem is critically dependent on achieving robust interoperability between disparate health information systems. This article examines the centrality of interoperability—the ability of different systems to exchange, interpret, and use data coherently—as a foundational challenge and enabler for modern digital health. The objective is to analyze the technical, semantic, and organizational dimensions of interoperability, assessing its impact on care coordination, public health surveillance, and innovation in healthcare delivery. Through a synthesis of policy frameworks, such as the HL7 FHIR standard, and real-world case studies on health information exchange networks, the article evaluates the progress and persistent barriers in connecting electronic health records, wearable devices, laboratory systems, and administrative databases. Results demonstrate that effective interoperability significantly enhances clinical decision-making by providing a comprehensive patient view, reduces redundant testing, empowers patients through accessible health data, and accelerates clinical research by enabling large-scale data aggregation. However, the conclusion identifies a substantial implementation gap, where technical standards alone are insufficient. Major obstacles include persistent data silos due to competitive and financial disincentives, unresolved privacy and security complexities in data sharing, significant upfront costs for system upgrades, and a lack of universal governance and trust frameworks. Achieving true "plug-and-play" interoperability is therefore not merely a technical endeavor but a complex socio-technical undertaking requiring aligned policy, sustainable business models, and a fundamental shift toward collaborative data stewardship across the entire health sector to unlock the full potential of digital health investments.

Interoperability, Health Information Exchange, Digital Health Ecosystems, Data Standards, HL7 FHIR, Care Coordination, Health Data Governance, System Integration