Electronic Government (E-Government) has become very important in recent years. It can be described as a system of digital interaction between a government and other parties, such as citizens, companies, employees, ministries and other government organisations. One of the most important elements of implementing E-Government systems is the interaction between users and E-Government systems, specifically the adoption and utilisation by those users, who are the main target of such systems. However, e-Government systems are still in the early stages in most developing countries including Saudi Arabia, and face many issues related to adoption, implementation and utilisation. Moreover, there is a lack of studies that investigate and analyse users' adoption and utilisation from different perspectives and also a lack of comprehensive frameworks specifically developed for such analysis. Thus, this research aims to investigate, analyse and understand the key factors that influence users' adoption and utilisation of e-Government systems and services in Saudi Arabia with a holistic approach. This could be used to enhance the current acceptance and use level and also would contribute to providing a user-centred path for designing and implementing new e-Services and government electronic systems. This study also aims to fill the knowledge gap in current e-Government literature about what might constitute a comprehensive framework on which to base such investigations. In order to achieve the research objectives, a comprehensive conceptual framework, namely, E-Government Adoption and Utilisation Model (EGAUM), was developed from a critical evaluation of several common models and theories related to technology acceptance and usage, in conjunction with a review of e-Government adoption literature. The developed model was then utilised to investigate and understand the influential factors on the adoption and utilisation of different types of users; namely, citizens, government employees and users from the business sector. A multiple method was employed in this research which includes a quantitative approach (as a main method) and a qualitative approach (as a supportive method). Several analysis procedures were employed, including descriptive and statistical analysis to validate the research model and to determine the significant influential factors. The results revealed that the user's Education Level, Perceived Benefits and implementing Regulations and Policies related to the e-Usage are common significant factors for the adoption and utilisation by all types of users. Moreover, the Functional Quality of Service/System, Perceived Simplicity and Socio-Cultural factors were found to be significant for the adoption and use of government employees and citizens. It was also found that Awareness plays a significant role in enhancing the adoption and use of public employees and users from the business sector. As a result of these findings, the research developed number of recommendations that can serve as guidelines for successful implementation of e-Government systems and services based on users' perceptions, attitude, beliefs, needs and choices.