The connecting link between the baseband unit (BBU) and the remote radio unit (RRU), in a centralised radio access network (C-RAN), is the fronthaul, which is the topic of this chapter. The fronthaul is presented as a key disruptive technology, vital to the realisation of 5G networks, but one with stringent requirements in terms of capacity, latency, jitter, and synchronisation. This chapter explains the fronthaul paradigm and presents an overview of legacy and new solutions in backhauling/fronthauling with critical analysis of respective advantages and limitations. In view of the debilitating expectations of 5G fronthaul performance, hybrid RAN architectures are also explored and analysed from their respective RAN gain and fronthaul requirements, leading to promising alternative RAN functional splits and innovations in X-hauling. The chapter delves into the (centralised) C-RAN/fronthaul versus (distributed) D-RAN/backhaul dilemma, offering a joint backhaul/RAN perspective and tangible trade-off analysis of the available options. The study advocates the need for a fronthaul architecture that is dynamic, adaptable, flexible, and expandable. To this end, a key catalyst to the realisation of the 5G fronthaul is equipping the network with self-optimisation and organisation (SON) capabilities that would timely adapt the network following the dynamically changing conditions. In this context, SON operation in the fronthaul becomes essential for optimisation objectives such as energy efficiency, latency reduction, or load balancing. Moreover, the SON-enabled joint RAN/fronthaul optimisation has a pivotal role in adjusting the level of centralisation according to the fronthaul capabilities and vice-versa.