The cosmic dawn and the epoch of reionization

In this chapter we briefly describe the physics behind the HI 21 cm line in terms of the interplay of the HI gas with the ionized plasma and the Cosmic Microwave Background, and the different phases the system undergoes as the ambient density and UV background evolve with cosmological time. We also address the problematics associated to the metal enrichment of the IGM and the implications for the models of galaxy formation and evolution. We briefly discuss possible synergies with other reionization probes like E-ELT, JWST and ALMA, and conclude by listing a number of cosmological scenarios describing some type of energetic injection in the Universe, scenarios to whose understanding SKA should be able to (at least partially) contribute.The authors acknowledge partial support from the Spanish Ministerio de Economía y Competitividad (MICINN) through projects AYA2013-48623-C2-2, AYA2007-68058-C03-01, AYA2010-21766-C03-02, AYA2012-30789, and the Consolider-Ingenio project CSD2010-00064 (EPI: Exploring the Physics of Inflation). We also acknowledge the support of the Ramón y Cajal fellowship (RyC 2011 148062) awarded by the Spanish MICINN and the Marie Curie Career Integration Grant (CIG 294183).Peer reviewe