This textbook reviews the theory, applications, and latest breakthroughs in Delay Tolerant Networks (DTNs). Presenting a specific focus on Opportunistic Mobile Networks (OMNs), the text considers the influence of human aspects, and examines emerging forms of inter-node cooperation. Features: contains review terms and exercises in each chapter, with the solutions and source code available at an associated website; introduces the fundamentals of DTNs, covering OMNs, PSNs, and MOONs; describes the ONE simulator, explaining how to set up a simulation project; provides detailed insights into the development and testing of protocols, together with a set of best practices for increased productivity and optimized performance; examines human aspects in the context of communication networks, from human-centric applications to the impact of emotion on human-network interplay; proposes various schemes for inter-node cooperation in DTNs/OMNs; presents a detailed discussion on aspects of heterogeneity in DTNs.