The EU has concluded that it needs a fully functioning and integrated internal electricity market to face the challenges of integrating renewable energy sources into the electricity grid. The European Commission has created guidelines for what the legislation is supposed to contain to create such a market. The so called grid codes are today around ten codes which successively are being implemented in national legislation for all member states. They regard connection-, marketand operation of the electricity grid and consists of several legal requirements for all member states. This study is divided in three parts. In the first part challenges with more renewable energy sources are described and the technical strategies that are suitable to solve those challenges. The second part describes an analysis of the connection- and operational codes on behalf of Ellevio, a distribution system operator in Sweden. They are interested in how the new legislation will affect their work and which new costs that will appear. The third part contains an overall study about the German electricity system since they have a lot of renewable energy sources in their production. The purpose was to see how they have handled challenges within their grid and their view on the new legislation. The overall result in this study was that the grid codes will change the role for Ellevio, which in the following years will have to handle higher information flow between grid users and Svenska kraftnät, which is the transmission system operator in Sweden. An another result was that the technical strategies are included in the legal requirements of the codes and that the legal requirements have been influenced to a great extent by the current German legislation.