This thesis is based on the implementation of a bilateral rural development program in Burkina Faso. The main purpose of this study was to put the actual implementation process of a bilateral development program in view. This was done by investigating how two dominant perspectives in the implementation literature can explain what in fact happens during the realization of an aid program. A further aim of the thesis was to explore the limitations of these two dominant theories, in order to get a full understanding of the complexity of the realization of an aid program. Based on the implementation theory, this study shows that the realization of an aid program can be understood from three different angles. Firstly, through a top-down perspective, we can understand the process as an implementation problem, where the organisation fails to put policy into effect. Secondly, from the bottom-up perspective, the importance of the formal decision is questioned. Consequently the implementation process can be explained by the interaction among those involved in an implementation structure where the implementation takes place. Thirdly, also from the bottom-up perspective, the implementation process can be seen as a negotiation process between those who seeks to put policy into effect and those upon whom policy outcome depends. The result of this study shows that the top-down, as well as the bottom-up perspective, can be useful to explain the implementation process of a bilateral program. Yet they cannot alone give us the full picture. The analysis from a bottom-up view plays an important role as it explores the complexity both within and between organisations, in which the complexity outside the control of the formal organisation is also discovered. Nevertheless, this perspective has its limitations. As it does not consider an explicit theory, it overlooks the factors that are affecting the behavior on the ground. The top-down analysis is interesting in the context of development cooperation as it analyzes whether an organisation has the capacity to put policy into effect. Yet the top-down approach has a rational way of examining the implementation process and does not reflect on different reasons for various behaviors. As this perspective is restricted to the formal decision, it fails to analyse what side effects the realization process can bring. Neither implementation theories take into account how institutional factors, in a global context, are influencing the local situation where the implementation takes place. This thesis argues that institutional factors (in terms of norms) could give complementary explanations to the implementation theories, in order to develop our understanding for the realization of a program. By regarding the implementation process as a part of a greater process of development cooperation, complementary explanations could be given about why actors behave like they do. Particularly within the actual context of strong changing trends among donors concerning how sustainable development can be achieved. This study claims that we could learn more about development programs as a whole by illuminating the implementation process itself. Considering the changes in development cooperation, in which the processes and ownership-based programs are gaining importance, the implementation theory is fruitful as it highlights the process.