Throughout its twenty-two year history, the authors ofPlant Physiologyhave continually updated the book to incorporate the latest advances in plant biology and implement pedagogical improvements requested by adopters. This has madePlant Physiologythe most authoritative, comprehensive, and widely used upper-division plant biology textbook. In the Sixth Edition, the Growth and Development section (Unit III) has been reorganized and expanded to present the complete life cycle of seed plants from germination to senescence. In recognition of this enhancement, the text has been renamedPlant Physiology and Development. As before, Unit III begins with updated chapters on Cell Walls and Signals and Signal Transduction. The latter chapter has been expanded to include a discussion of major signaling molecules, such as calcium ions and plant hormones. A new, unified chapter entitled Signals from Sunlight has replaced the two Fifth-Edition chapters on Phytochrome and Blue Light Responses. This chapter includes phytochrome, as well as the blue and UV light receptors and their signaling pathways, including phototropins, cryptochromes, and UVR8. The subsequent chapters in Unit III are devoted to describing the stages of development from embryogenesis to senescence and the many physiological and environmental factors that regulate them. The result provides students with an improved understanding of the integration of hormones and other signaling agents in developmental regulation.