This book provides a comprehensive review of all aspects of the molecular and cell biology of abscisic acid (ABA) metabolism, transport and signal transduction, covering our current understanding of ABA as well as research trends. The agricultural significance of ABA metabolism, transport and signal transduction is also discussed. The phytohormone ABA regulates many aspects of plant development and plays a central role in plant adaptation to environmental stresses. Over the past few decades, considerable advances have been made in the study of ABA metabolism, transport and signal transduction, greatly deepening our understanding of the underlying mechanisms of ABA function at the molecular, cell and whole-plant level