This module describes the nature of genetic resources for food and agriculture, with special focus on forest genetic resources. As mentioned in the Millenium Ecosystem Assessment (MEA), forests are home to the vast majority of the Earth’s terrestrial biodiversity (MEA, 2005), and trees are the keystone species of forest ecosystems. Forest trees and other woody plant species provide wood, fibre, fuel and many non-wood forest products. They also contribute to a broad range of ecosystem services and fulfil environmental functions. Globally, around 2 400 species of trees, shrubs, palms and bamboo are actively managed for products and/or services, and approximately 700 tree species are subject to tree improvement programmes (FAO, 2014b).