The design of ICT-based application traditionally focuses on the analysis of relationships between ICT performances, user or application requirements and costs. However, the climate change, the environmental pollution, the earth resource depletion, the energy price increase forced ICT sector to analyse and to consider these issues as new requirements in the development of ICT solutions. The specification of environmental measurements is then necessary in order to be able to correctly assess the performances of so-called green ICT systems. In this chapter, ICT metrics and environmental metrics are presented. The social responsibilities of ICT companies in the context of sustainable development are then developed. Finally, from an example, a general methodology for eco-designing ICT systems is proposed. It is based on systems engineering enabling to analyse the system as a whole in integrating the metrics previously described.