My main research field concerns cosmic reionization and the physics of the high redshift Universe during the transition phase that marks the end of the“Dark Ages”. In particular I focus on the science of the 21cm hyperfine transition of neutral hydrogen. In the near future the neutral InterGalactic Medium (IGM) prior and during cosmic reionization will be directly studied through 21 cm observations by next generation radio telescopes. I also investigate the effects of Dark Matter (DM) decays/annihilations on the high redshift IGM properties, and as a consequence on the 21cm line. The most popular DM candidates can in fact be constrained if they leave different imprints on the IGM.