Vehicular communications are emerging as a promising technology to enable communica- tions using vehicles as network nodes. VDTNs appear as a novel approach to enable services and applications where it is not possible to de ne an end-to-end path. To allow communications in such challenging environments, VDTNs rely for their operation on cooperation between network nodes, which contributes to increasing network connectivity and improving overall net- work performance. To accomplish such a task, nodes may be asked to share their constrained storage, bandwidth, and energy resources with one another. However, nodes may be unwilling to cooperate in order to save resources or due to selfish behavior. This kind of node severely affects the network functionality. This article gives an overview of the eld, providing motiva- tions, challenges, and an evaluation of the impact of cooperative measures on the performance of VDTN networks.