The plant hormone auxin, or indole-3-acetic acid (IAA), is a central regulator of plant growth and development. Unique for auxin is its polar cell-to-cell transport (‘Polar Auxin Transport’, PAT) by which maxima and minima of this hormone are generated that direct patterning of embryos and tissues,, initiation of new organs, and a plant’s growth in response to environmental signals. This workshop brings together team of experts and young researchers, and aims to make a start with applying a similar joint modeling-experimental approach to aspects of PAT that are still poorly understood, with the objective to force a breakthrough with this method on the longer term. Unsolved issues can be suggested during registration from which a selection will be made at the start of the workshop. One important unsolved issue is how auxin moves inside the cell. Another issue is the function of the different auxin transporters in long distance basipetal or acropetal transport in respectively the shoot or the root. During the workshop we will discuss these topics in an open atmosphere and develop first versions of new models.