Plant hormones influence several important aspects of plant growth and development. Most of our knowledge about function of plant hormones comes from mutational analysis using the model plant Arabidopsis thaliana. Forward genetics is a powerful tool for identifying mutants that are involved in particular hormone signaling pathways. Mutants with altered hormone response were commonly used to study hormone biosynthesis, to dissect the molecular genetics of hormone signaling pathways, and to isolate the corresponding genes. For particular interest, first chapter of this book focused on jasmonic acid and auxin, and their functions in plant growth and development. Second part explained how current tools of molecular biology can be applied to dissect complex hormone signaling pathways. The last part involved in determining suppressors of a specific hormone signaling mutant and its genetic analysis to find new components of specific hormone signaling pathways that cannot be determined by direct hormone screening. This book will be a cross reference, especially for young researchers who just entered this fascinating world.