As a prospective intelligent transport systems (ITS) technology, vehicular ad hoc networks (VANETs) have recently been attracting an increasing attention from both research and industry communities. These networks have no fixed infrastructure and instead rely on vehicles themselves to provide network functionality. In this paper we review the related literature on VANETs characteristics and provide more insight on multi-hop inter-vehicle communication. We explore VANETs with respect to key enabling technologies ranging from physical radio frequency, MAC/PHY layer, routing strategies, security and privacy to mobility modeling and simulation study. Then we outline current state of research and open issues.