Abstract: The background to the use of the expression "green tribology" is given. The definition, objectives and main mission of green tribology are presented. The fields of the green tribology in a narrow sense and in a broad sense are also clarified. Moreover, through introducing the recently advances in green tribology, its research contents are discussed comprehensively from four aspects : (1) Tribological theories, methods and technologies for saving both energy and materials, and prolonging the working life of tribological parts and tribo-systems; (2) Tribological theories, methods and technologies for removing or reducing the harmful effects to ecological balance (including human health) produced by both tribological parts and tribo-systems in the course of life cycle; (3) Research on the tribological aspects of natural environment and natural disaster, mainly focused on the role, mechanisms and effects of friction; (4) Tribological technologies for providing technological support to the equipment of both renewable and clean energy. The developing directions of green tribology are also pointed out. It is held that green tribology will certainly play an increasingly important role as the earth is facing with serious energy and environmental problems.