Leaves are the leading source of carbon for plant growth and reproduction, and possess a wide range of protection systems against environmental stress. The leaves of the coffee plant, characterized by a high antioxidant potential, have a significant impact on fruit quality, and identifying markers in leaves for plant adaptability to environmental stress provides an indication of the quality of future fruits. This chapter provides an inventory of molecules identified to date in the leaves of cultivated coffee trees. It describes the beneficial effects of the molecules exclusively found in leaves on both plant physiology and human health, and suggests where future trends of research in this area may lead.