Plant bioregulators (PBRs) are used extensively in the tree fruit production industry. They influence many processes in a plant including shoot growth, branch angle, bud break, flower bud formation and fruit abscission, ripening, shape and finish, and as such can be used to optimize not only plant growth but also fruit yield and quality. The chapter starts with a classification of PBRs, followed by a detailed discussion on the application of PBRs and their use such as in the development and maintenance of tree structure, and also the control of vegetative growth. The use of PBRs in crop load management and their influence on flowering and fruit set is also presented concluding with sections on both the pre-harvest application of PBRs and their use in improving fruit shape and appearance.