The integration of renewable energy resources - as key enablers for the reduction of greenhouse gas emissions into the power systems - has increased over the past years and led to higher complexity of electric power systems. The increased availability of advanced automation and communication technology, along with novel intelligent solutions for system operation has transformed the traditional power system into a cyber-physical energy system - a smart grid. In this context research and technology development are important to turn the existing energy infrastructure into a sustainable one. A major role in all these developments are research infrastructures in the domain of power and energy systems. This presentation provides an overview of achievements, experiences and lessons learned from European smart grid and distributed energy resources research infrastructure projects gained over more than a decade so far.