Plant growth regulators are the signaling molecules produce in minute quantities. Different concentration of hormones conciliates range of developmental processes in plants depending upon tissue sensitivity and environmental factors. This chapter concerned with five classic hormones- auxin, gibberellins, cytokinin, abscisic acid and ethylene. More recently explore compounds that have regulatory role in plant development are jasmonic acid, brassinosteroids, salicylic acid and strigolactones. Each hormone has their own particular pathways for regulation, biosynthesis and catabolism.