Traditional networks suppose the existence of some path between endpoints, small end to end round-trip delay time, and loss ratio. Today, however, new applications, environments and types of devices are challenging these assumptions. In Delay Tolerant Networks (DTNs), an end-to-end path from source to destination may not exist. Nodes may connect and exchange information in an opportunistic way. This book chapter presents a broad overview of DTNs, particularly focusing on characteristics, challenges, and research projects on this field. In the near future, cars are expected to be equipped with devices that will allow them to communicate wirelessly. However, there will be strict restrictions to the duration of their connections with other vehicles, whereas the conditions of their links will greatly vary; DTNs present an attractive solution. Therefore, VDTNs constitute an attractive research field.