There is worldwide demand for the implementation of electronic health systems and a transformation to electronic transactions in healthcare organisations. This move to ehealth transformation stems from the perceived positive impact that e-health systems have in improving the quality of healthcare and, in turn, reducing expenses. Despite this, more than half of previous Electronic Health Record System (EHRS) implementation projects have failed due to several barriers and challenges. There has been no previous research that has explored the implementation of an EHRS in Primary Healthcare Centres (PHCs). In addition, barriers and facilitators to the implementation of large-scale EHRS in PHCs are not well defined and there is little known about the impact of Financial Resources (FR) and Centralised Management (CM) on such implementation. Thus, this thesis aims to explore the large-scale implementation of EHRS in PHCs in Saudi Arabia (SA). To achieve this aim, a mixed-methods approach comprising both quantitative and qualitative methods was adopted. Data were collected via questionnaire-based studies and semistructured interviews. Three different populations were targeted: project team members, PHC staff, and EHRS end-users. Descriptive and inferential statistics were applied to the quantitative data, and thematic analysis was used to analyse the qualitative data. The findings revealed high PHCs readiness at the organisational and individual level when compared with the technological level. Both FR and CM were documented to have a positive impact on the implementation of a large scale EHRS. Several facilitators to the implementation of the EHRS were identified, including: strong leadership and appropriate management, PHC specifications, system usability, perceived usefulness and efficiency. The scale of the project, shortage in Health Informatics (HI) expertise, lack of training and support, geographic challenges, software selection and end-user involvement were identified as the main barriers to implementing a large-scale EHRS in the PHCs. No relationships were detected between individual demographic differences, such as age and gender, and level of readiness or satisfaction. Based on the Saudi experience, there may be some important transferable lesson for similar projects elsewhere. Large-scale EHRS projects need to adopt CM. In addition, due to shortage in HI expertise, policymakers may need to carry out some consultations to formulate good implementation plane. Largescale projects also need to be implemented by more than one vendor and include training and technical support to increase end-user satisfaction. Inadequate infrastructure, lack of interoperability, changing executives and lack of technical support were the main possible causes to the failure of large-scale EHRS projects. Implementation needs to ensure sufficient budget and time have been allocated to mitigate the challenges identified. III DECLARATION