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Opportunistic or delay‐tolerant networks (DTNs) may be used to enable communication in case of failure or lack of infrastructure and to complement existing wireless technologies (cellular, WiFi). This chapter identifies and discusses the three main characteristics of opportunistic networks, around which all forwarding schemes are designed and optimized. It focuses on the first aspect and shows how replication and coding techniques are used to improve delivery performance, without explicit knowledge about past or future contacts. Then, the chapter discusses how contact patterns can be inferred by observing and maintaining some statistics about past contacts, and how simple or more sophisticated techniques can be used to predict future ones, based on collected knowledge. It presents some examples of opportunistic routing scheme, which are considered to be state of the art, that exploit both replication and …