Governments have been undertaking digital transformation for many years to offer new ways of interaction to their constituents. However, they face different challenges to migrate users towards digital channels and electronic documents, which are believed to be more cost-efficient for all. Based on the literature review, it is identified that research has been mainly focused on exploring and validating factors influencing acceptance and adoption of e-government self-service applications, and in general it has been conceived it as static phenomenon. Consequently, there is still a lack of "holistic" understanding of the dynamics of the uptake of e-government services. This thesis presents the research process and the results of a longitudinal critical realist case study conducted in the field of e-government with the aim of understanding the uptake process of inter-organizational e-government services by micro-enterprises. This study moves beyond identifying a list of factors influencing adoption at specific point in time. It offers a mechanism-based explanation, and it captures the processual dynamics of e-government services uptake from microbusinesses perspective in a context of mandatory usage of electronic invoicing. The proposed explanatory theoretical framework for the uptake of inter-organizational e-government services by microbusinesses consists of four phases: information seeking, adoption decision and acquisition, implementation, and use and maintenance. Each stage suggests the presence of mechanisms that interact among them and explain the events that occurred during each phase, and the advance towards the next stage. Eight mechanisms were identified: experience, regulatory, market, intermediation, affordance, expectation, appropriation, and administrative literacy mechanism.