## 1 Introduction  
Gaia-X ([[https://www.gaia-x.eu/](https://www.gaia-x.eu/)]([https://www.gaia-x.eu/](https://www.gaia-x.eu/)) (accessed on 5 December 2024)) is a European initiative aimed at creating a sovereign data infrastructure. Launched in 2019, it seeks to establish a federated ecosystem where data can be shared and processed securely and transparently within Europe. The project aims to ensure data sovereignty by keeping data within European borders, protecting it from foreign influence, and promoting European technological leadership ([[https://digital-strategy.ec.europa.eu/en](https://digital-strategy.ec.europa.eu/en)]([https://digital-strategy.ec.europa.eu/en](https://digital-strategy.ec.europa.eu/en)) (accessed on 5 December 2024)). Gaia-X also emphasizes interoperability and standardization to facilitate data exchange between different platforms and providers. It is a key initiative shaping the future of the Internet, by building a trusted, decentralized, and interoperable digital ecosystem that emphasizes data sovereignty, security, and transparency--crucial elements for the future Internet. By enabling federated cloud services and promoting European standards, Gaia-X can contribute to a more open, secure, and user-centric Internet, which aligns with the goals of the future Internet vision, where data flow freely but securely across borders, industries, and applications. Gaia-X is a highly complex initiative, with numerous white papers detailing its architecture, principles, and vision for a federated European data infrastructure. While some early implementations have emerged, demonstrating the potential of Gaia-X in sectors like cloud services and data sharing, building fully Gaia-X-conformant solutions remains a significant challenge. The intricacies of aligning with its strict standards, such as data sovereignty, interoperability, and transparency, present hurdles for businesses and developers. Moreover, the integration of diverse cloud providers, adherence to Europeanregulations, and ensuring seamless data portability across borders further complicate the path to widespread Gaia-X adoption. Within the framework of the project Gaia-X-Med, we explored the application of Gaia-X concepts within the healthcare sector, in order to analyze how the Gaia-X infrastructure can drive innovation in healthcare, improve patient outcomes, and support the development of personalized medicine, while maintaining compliance with strict regulatory frameworks like GDPR (General Data Protection Regulation (https://gdpreu (accessed on 5 December 2024))). By leveraging Gaia-X's principles of data sovereignty, security, and interoperability, Gaia-X-Med aimed to facilitate secure data sharing and collaboration between healthcare providers, researchers, and medical institutions. In six use cases, the project addressed critical challenges such as ensuring patient data privacy, enabling cross-border data exchange, and enhancing access to medical information for research and treatment purposes. This paper presents the main results of Gaia-X-Med. It evaluates the Gaia-X approach for its ability to enable data exchange in service ecosystems, as applied to six use cases from the health domain. In order to do so, we adapted the Gaia-X concepts to fit the requirements of those use cases, and we report on the results and a number of lessons learned. The remainder of this paper is structured as follows: Section 2 gives an overview of existing approaches for realizing data sovereignty and trust, and presents existing software implementations. Section 3 introduces the Gaia-X-Med project and outlines the framework for the six eHealth use cases examined, highlighting their unique requirements and relevance to Gaia-X principles. Section 4 delves into the core Gaia-X concepts, including the modifications made to align with healthcare-specific demands. In Section 5, we provide a detailed analysis of the Gaia-X-related implementation of these use cases, with a focus on ensuring trust and secure data sharing within federated healthcare networks.