Lobbying as a function to influence political decisions got more and more important within the last three decades. However, especially the German speaking area considers it as a bad and negative function that changes or even makes politics at discretion with largely corruptive methods. In the process of this master thesis I want to analyze if it is indeed like that by analyzing the matters of lobbying, transparency and democracy in more detail. The European Union and its decision-making institutions, i.e. the European Commission, the European Parliament and the Council of the European Union, are the basis for this research process, which is why they are discussed in detail with regard to lobbying, transparency and democracy. In a general and primarily theoretical discussion about these matters, the term lobbying, its purposes, actors and methods as well as the principles of transparency and democracy are analyzed, explained and connected to the legal basis of the European Union and its institutions. By doing so, possible improvements and recommendations to strengthen these principles are outlined. Additionally, the situation and the legal basis of the USA is discussed and compared to that of the EU and its institutions. Besides this general research process, the General Data Protection Regulation unveiled by the European Commission in 2012 is analyzed in detail to figure out the influence of lobbyists on the European Union's ordinary decision making procedure. As a result of strongly diversified interests that had to be taken into account the regulation needed more than four years for a final decision that will in any case take place in 2016. In internal circles it is known as one of the, if not the most lobbied legislative act in the history of the EU. How far lobbying influenced the original principles of the regulation and what this influence means for the individual legitimacy of the European decision-making institutions and the legitimacy of the European Union as a supranational construct should be clarified in this analysis. In a brief conclusion it can be said that lobbying is a legitimate function needed in every democracy. It is not only used by associations, corporate actors, all kinds of organizations or other actors, but also by politicians. However, due to the fact that in particular corporate actors have lots more resources and possibilities on their disposal it needs rules and regulations as well as a maximum on transparency during the decision-making procedures to protect the fundamental principles of a democratic system. As it is shown by way of analyzing the General Data Protection Regulation, the EU and its institutions sometimes lack in this field, hence why they should act to provide better legitimacy towards their the citizens of the member states.