The plant hormone auxin plays a fundamental role in the growth and development of plants. Researchers from across the globe are currently attempting to unravel the molecular mechanisms by which auxin controls such diverse processes as cell division, cell elongation, and differentiation. Research questions on auxin action are being addressed using state-of-the-art techniques that are available to cell biologists, geneticists, molecular biologists, biochemists, and physiologists. This text highlights many of the major topics that were covered in a recent workshop that was specifically focused on research into the mechanisms of auxin action. The articles in this text give a current update of the research findings on auxin biosynthesis, metabolism and transport; evolutionary patterns; auxin perception, signal transduction and physiology; auxin-regulated gene expression and protein degradation pathway in auxin responses; and cross-talk between auxin and other plant signalling pathways.