Vehicular ad hoc networks (VANETs) have attracted a lot of attention over the last few years. They have become a fundamental component of many intelligent transportation systems and VANETs are being used to improve road safety and enable a wide variety of value-added services. Many forms of attacks against VANETs have emerged recently that attempt to compromise the security of such networks. Such security attacks on VANETs may lead to catastrophic results such as the loss of lives or loss of revenue for those value-added services. Therefore making VANETs secure has become a key objective for VANET designers. To develop and deploy secure VANET infrastructures remains a significant challenge. The authors discuss some of the main security threats and attacks that can be exploited in VANETs and present the corresponding security solutions that can be implemented to thwart those attacks.