Global warming and climate change trends call for urgent action to manage information and communication technologies in a sustainable manner by minimizing energy consumption and utilizing resources more efficiently. Distributed computing environments have become the de facto platforms for many applications. These systems bring a range of heterogeneous resources that should be able to function continuously and autonomously. However, distributed systems expend a lot of energy which raises a range of important research issues related to the use and virtualization of ICT resources in a way offers significant potential to contribute to the goal of what has been described as ‘green computing’. This paper will review some of the important questions related to the development of new algorithms and tools for energy–aware resource allocation for large–scale distributed systems enabling these systems to become environmentally friendly.