VANET is short for Vehicular Ad hoc NETwork. Vehicular Ad-Hoc Networks (VANETs) are a special class of Mobile Ad-Hoc Networks (MANETs) where nodes self-organize and self-manage information in a distributed fashion. They consist of vehicles and/or roadside units that assist in the management of the network. A public key infrastructure (PKI) was widely adopted by recent research efforts as a solution to security problems. One part of a PKI solution is certificate revocation. Certificate revocation is one way to terminate the membership of a vehicle from the network. Revocation can also be conducted by the other vehicles participating in the network. This paper is a survey of different revocation schemes developed for VANETs. The purpose of the paper is to survey the literature, and provide an overview of the extent of the research done in the area of revocation in VANETs.