With an intricate biosynthesis pathway and a complex gene signalling cascade, auxin is involved in many biological processes, including plant growth and responses against potential pathogens. In this book, the authors present topical research in the study of the structure, biosynthesis and functions of auxins. Topics discussed include the roles of auxin during plant-microbe interactions; auxin biosynthesis and function in plants; chemicals as adjuvants in auxin induced adventitious rooting; and the effects of auxins on plant pathogenic phytoplasmas and phytoplasma-infected hosts.