The EU Climate and Energy package, setting the 20-20-20 targets of future energy systems by 2020 will change the landscape of future energy system in Europe and worldwide. A transition from monopolised controlled Power network to customer oriented Smart Grids operating in deregulated energy markets poses several regulatory, organizational and technical challenges. To that end several international Smart Grid projects have been launched worldwide in EU, the US and China. To cope with the inherent complexity of Smart grid systems the systemic property of Interoperability has been proposed by organisations such as NIST and GridWise in the US and is also adopted by EU. Interoperability of smart grids entails design, implementation, validation and maintenance of systems ensuring technical, information, and organizational interoperability. In order to address Quality of Service (QoS) in this setting, the tool of Service Level Agreements (SLAs) has been proposed. A SLA set up the coordination between stakeholders in a business case and relevant services with set-points and agreements to be monitored. A challenge is to identify relevant (new) stakeholders, their competences and roles in the business case. In the thesis we specifically address the following issues: • Empowerment of end-users • Trustworthy integration of DER- Distributed Energy Resources in delivered services • Validation (Interoperability) of SLAs To those ends, we have implemented an experimental test bed based on Multi-agent systems and sensor technologies. The thesis concludes with assessments of our findings and some pointers to future work. Our work is validated scientifically and industrially by participating in the two EU project INTEGRAL and SEESGEN-ICT , both ended in late spring 2011.