Despite great advances in our understanding of the environmental, social and economic role of trees in farming systems, much remains to be done, especially regarding the wider adoption of agroforestry and its up- and out-scaling. This chapter explores the relationship between trees, science and global society. The chapter offers an overview of tree agroecology, tree domestication, commercialization of trees and the relevance of development studies to this field. The chapter assesses the potential for upscaling the exploitation of trees as a sustainable resource and examines relevant issues connected with policy and agribusiness.