Sundhed.dk facilitates patient-oriented digital services which provide access to and information about the Danish healthcare services. Since its launch in 2003, sundhed.dk provides several functionalities such as quality assured health information, access to medical records and medication, and an overview of the Danish healthcare system. Sundhed.dk creates linkages between existing data sources, opens up data sets to new user groups, and facilitates communication between healthcare providers and citizens. The portal also ensures further development not only by providing a secure infrastructure, search optimization, and user interfaces, but also by supporting the development of new services.Sundhed.dk has earned good reputation and high standing in the healthcare sector internationally. Health authorities from other countries, that wish to build similar solutions, have approached sundhed.dk for advice and best practice (Sundhed.dk 2014a). However, the positive reputation and high level of maturity of sundhed.dk has not been established overnight. Thus the assumption by other countries of simply copying the code, the user interface, and the technical infrastructure is far too simplistic if they wish to attain what Denmark has achieved with respect to e-health services for citizens. Other infrastructural resources in place, including existing systems, regulations, communication standards, as well as organizational structures in the Danish healthcare sector, have played a vital role in establishing the national 210 e-health infrastructure (Thorseng and Jensen 2015). Consequently, the design, development, and implementation of an e-health initiative such as sundhed.dk, that has become an integrated part of a national infrastructure, becomes relevant to study.In line with the aim of the book, this case chapter provides insights into the role of the installed base -i.e., pre-existing technologies, regulatory frameworks, data resources, and organizational arrangements -in the evolution of sundhed. dk. In particular, we argue that the main reasons for the current positioning of sundhed.dk have been its ability to (1) collate and assemble existing data resources, (2) repurpose and enhance current data sources in the health sector, and (3) engage a multiplicity of stakeholders. We argue that these activities represent three ways of capitalizing on the installed base that has led to the evolution and current situation of the e-health portal. At the same time, we show how these three modes come with a number of challenges for sundhed.dk in its pursuit of further innovation.The rest of the chapter is organized as follows. We start out by introducing the Danish healthcare sector to set the context for sundhed.dk. Further, we describe the development of sundhed.dk, its purpose, as well as its current organization. Based on this description, we analyze how the organization behind the e-health portal succeeded in establishing a national healthcare infrastructure by assembling existing data resources, repurposing current healthcar...