This research studies the interaction between eHealth and implementation success. eHealth has become an important subject of discussion and evaluation for healthcare organisations over the last decade or so, and has also been the focus of national healthcare programs and plans. Billions of pounds are being spent on implementations of eHealth. Those implementations endeavour to cut costs, while at the same time, achieving enhanced efficiency and accuracy. Hence, understanding success in eHealth has become an attractive topic for research and a requirement in healthcare practice. This research aims to understand the definitions and factors of success in implementations of eHealth. In doing so, it examined the suitability of the Delone and McLean Information Systems (D&M IS) success model to explain eHealth success. A multistage research design was adopted. The first stage was composed of a thorough Systematic Literature Review that covered the origins and development of eHealth, the different themes in the research around eHealth, the concept of Critical Success Factors in IS, and the available frameworks for IS implementations, in general, and eHealth, in specific. As for the second stage, which constituted the core of this study, it was based on an exploratory, mixed-methods approach to research where a triangulation of research methods, data collection tools, and data sources was employed. As part of this approach, two case studies were conducted. Within the case studies, 20 semi-structured interviews were carried out; the outcomes of the interviews were analysed using framework analysis. In addition, a survey took place, and feedback from the survey respondents was analysed using different quantitative statistical methods. Finally, content analysis was relied on to examine all the relevant existing documentations. This research found that information systems success models, already in existence, can facilitate the understanding of implementation success in eHealth. The D&M IS success model, in particular, was chosen and applied. The results of the qualitative and quantitative research showed that the D&M model is suitable to explain and define success in eHealth. In addition to the constructs that define success in eHealth, such achievement is attributed to a number of factors. This research found that eHealth shares a number of success factors with other IS implementation frameworks. At the same time, eHealth success factors that emerged from the case study, like; clinical engagement, the role of eHealth leadership, and clinical champions are discussed. This research led to the exploration of new factors that require a better understanding, such as; the effects of a national eHealth policy, the role of critical champions, and innovative methods of eHealth training. Links between eHealth success definitions, and success factors were investigated, as part of this study. The results of this research revealed statistically significant links between the achievement of organisational goals and user satisfaction, and ultimately, with implementation success. This work has allowed for the development of a potential eHealth specific version of the D&M model as a provisional model to be confirmed with further research. It identified success factors that affect the implementations of eHealth. Some of the factors are eHealth specific, which can also be developed into a provisional model. In addition, this work has resulted in a number of recommendations for implementers and evaluators of eHealth in practice.