Plant hormones play a crucial role in controlling the way in which plants grow and develop. While metabolism provides the power and building blocks for plant life, it is the hormones that regulate the speed of growth of the individual parts and integrate them to produce the form that we recognize as a plant. In addition, hormones play a governing role in the process of reproduction. This text is a description of these natural chemicals: how they are synthesized and metabolized, how they act at both the organismal and molecular levels, how we measure them, and a description of some of the roles they play in regulating plant growth and development. This is the second edition of the text published in 1987 under the title Plant Hormones and Their Role in Plant Growth and Development . All chapters have been rewritten to include the latest information on plant hormones, and several totally new chapters have been included, particularly with reference to the molecular biology of plant hormones. The book is a collection of newly written, integrated and illustrated reviews describing our knowledge of plant hormones and the experimental work that is the foundation of this information. It is directed at advanced students and professionals in the plant sciences: botanists, biochemists and molecular biologists, and those involved with the horticultural, agricultural and forestry sciences.