The evolution of wireless devices, such as laptops, personal digital assistants (PDAs), and cell phones, has changed the way networking and communication are perceived. The growing dependence on these devices, along with the high mobility of users, has increased the need to be connected in all places at all times. This increase in user demand, along with the evolution of new applications such as satellite networks, sparse mobile networks, and remote disconnected communities, has ultimately led to the rise of the delay and disruption tolerant networks (DTNs) research area. The future of computer networks includes an Internet that encompasses numerous heterogeneous networks, reaches out to the most remote areas, and provides communication in the most extreme and unstable conditions. With such a vision, new problems with large complexities arise. Communication devices in the future will be required to remain connected despite the rise of new challenges such as network partitioning, intermittent connectivity, large delays, the high cost of infrastructure deployment, and the absence of an end-to-end path. This book is an initial attempt to address these challenges.