In response to incoming action potentials the presynapse exocytoses neurotransmitter filled vesicles. Proper information encoding requires that the release occurs exactly at the junction to the postsynapse, that it is temporally tightly coupled to the electrical signal and that it proceeds efficiently. This review discusses the structure and function of the active zone, which is defined as the region of the presynapse that is specialized for vesicle release. Particular emphasis is put on the molecular players that control spatial restriction, efficiency and timing of exocytosis in the mammalian nervous system.