The last 10 years have witnessed an explosion in our understanding of plant h- mones. The often vague models of hormone action developedover decadeshave been replaced in short order by detailed molecular models that include receptors and in many cases downstream signal transduction components. Given the rapid progress in understanding the mechanism of action of plant growth regulators, a technical review of hormone methodology is timely. Our book focuses on genetic, biochemical, ana- tical and chemical biological approaches for understanding and dissecting plant h- mone action. The greatest strides in plant hormone biology have come, by and large, from the use of genetic methods to identify receptors and we dedicate a chapter to general genetic methods of analysis using the model system Arabidopsis thaliana. A cluster of chapters focuses on biochemical methods for documenting interactions betweenhormonesand their receptors. Theimportance of these assays is tremendous; receptor–ligand interactions in animal model systems have been the cornerstones of pharmacological and medicinal chemical assays that have enabled identification of selective and non-selective agonists and antagonists that can be used to further probe and dissect questions of receptor function. This is likely to be a major new frontier in plant hormone research.