Following the reactor disaster of Fukushima in 2011, the Federal Council has developed the Energy Strategy 2050. With it, an energy regime that enables the progressive withdrawal from nuclear energy production and the expansion of renewable energy sources should emerge in Switzerland. However, every transformation of the energy system has implications for a significant number of stakeholders. On the one hand, the federal government, cantonal and municipal administrations are responsible for the implementation of political requirements and have potential to advance the transformation of the Swiss energy system. On the other hand, the energy companies play an important role in development, engineering and construction of the projects. At the same time, the population is also concerned by the energy system transformation and approves it on national, cantonal and communal referendums. Finally, in the acceptance of the energy projects, interest groups play an important role as well, especially during consultation procedures, parliamentary debates or referendum campaigns. When involved in a policy process, they face the important strategic choice between either joining forces with others or working alone. Therefore, this may have an impact on their effective influence on political decision-making. For instance, interest groups can form longterm coalitions with the same policy actors or collaborate with each other only on a particular decision. Moreover, active cooperation contributes to a share of resources and information between partners. Thus, it may potentially boost lobbying success of the weaker advocates by compensating for low financial and staff resources (Junk, 2020). In this Master's thesis, we examine whether the cooperation between interest groups and policy actors increases their lobbying success. Precisely, we analyse the interest groups' cooperation and their success in two acceptance processes of the wind energy projects in Switzerland. The research design of this Master's thesis is innovative for two reasons. First, previous studies used to focus on one type of the cooperation network. For instance, several researchers examined the influence of the advocacy coalition on the final policy outcome (Sabatier, 1998; Jordan, 1990), while others analysed the advocacy success of the interest groups as part of inter-organisational networks (Beyers and Braun, 2014) or ad-hoc issue coalitions (Mahoney, 2007). However, few studies looked into the connection between different types of the cooperation network. In the present Master thesis, we used two approaches to define a “lobbying coalition”: a preference similarity approach and an organisational approach. The first approach focused on positional “camps” on an issue, while the second one identified the ties between organisations as general organisational characteristics (Junk, 2019c). Second, our project is innovative because we examined the correlation between the interest groups' strategies and their success in the wind energy promotion process in Switzerland, particularly in the canton of Neuchâtel. Previous researchers focused more on social acceptance of the wind energy projects in Switzerland. For instance, Ebers and Wüstenhagen (2017) examined the influence of procedural and distributional justice on social acceptance of wind parks in Switzerland. They determined that minimizing ecological impacts of the wind projects could significantly increase their social acceptance. Earlier, Götz (2014) explored the relationship between general attitudes toward wind energy, local acceptance of specific wind projects and respective intentions to act on those attitudes in Switzerland. However, Kriesi and Jegen (2001) conceptualized the actor constellation in the Swiss energy policy domain in 1998. They particularly focused on the configuration of power in a period of transition between two policy equilibra. In Switzerland, wind energy is perceived as green and renewable. Moreover, it has the backing of the Federal Council and Parliament, which in 2006 declared it to be in the country's interest. Nevertheless, it faces a strong opposition from several local and national environmental associations due to concerns about landscape preservation and negative effects on ecosystems. This is the reason why we find it interesting to analyse the strategies used by organisations to block or move forward the decision-making on wind energy projects. In the next section, the important key concepts are defined and the literature review on the relationship between the interest groups' cooperation and the advocacy success is presented. Moreover, this includes the formulation of four hypotheses. Then, the main variables, measurements and data sources for the empirical analysis are described. Thereafter, each hypothesis is tested using two different analyses: the Social Network Analysis and the documentary analysis. The comparison of the empirical results follows. Finally, the main findings are summarised and put into perspective in the conclusion.