In most sensory systems, neuronal connections are arranged such that neighboring points in the peripheral organs (e.g. eye) are represented by adjacent locations in the target region of the brain. Mechanisms by which such topographic projections are established had been a main focus of developmental neurobiology for many years. How do growing axons know their exact place ("address") to terminate? What principles and molecules are at work to set up topographic maps? In this class, I will discuss cellular and molecular mechanisms for topographic map formation, covering the classic work by Sperry as well as the subsequent identification of topographic "labels".