With the emergence of large scale distributed systems (Data Centers, Grids, Clouds...), the amount of energy (watts) required for high performance distributed computing and networking becomes a real challenge. Taking into account of an efficient energy usage will have an impact on how we design architectures, services and protocols. Various GREEN-* approaches ("Green Computing", "Green networking", "Green programming"...) are currently proposed by academics and industrial consortiums. This talk will review current challenges and solutions associated to energy efficiency approaches in distributed systems.