Data delivery provided data transmission services for various applications over Vehicular Ad Hoc Networks (VANETs). In particular, it was an indispensable component in the vehicle active safety systems, urban life services, and emergency rescue applications. However, it faced such challenges as brought by the rapid changing of network topology, frequent network partitions, and the limited wireless channel capacity. The paper analyzed the characteristics of VANETs, pointed out the main influencing factors in the VANET data delivery, and then reviewed the existing technologies, including the basic implementation approaches and the optimization strategies for improving the capabilities of data delivery.