Abstract of his talk: Root architecture is a trait that strongly contributes to the performance of plants. The way plant root systems colonize the soil will be determinative for the all or not thriving growth of the above ground parts. Because plants are sessile organisms, the exploration of soil in search of water and nutrients is mainly dependent on steering and controlling cell division and elongation. The presence of an endogenous tissue layer in which, on a regular basis, stem cells with high cell division competence are deposited represents a powerful instrument through which plants can easily generate new lateral root branches. These branches are not arbitrarily formed along a root axis, but their spacing is rather determined by an endogenous patterning mechanism. Furthermore, it only rarely happens that lateral roots are formed close to each other. Both, the endogenous patterning mechanism combined with lateral inhibition signals guarantee an even distribution of lateral organs over the entire length of the root. New insights in these patterning mechanisms will be discussed with the emphasis on putative cellular and tissue communication systems that are involved.