The phase transition by which the cosmic gas turned again into an ionized 
state after  recombination is dubbed Cosmic Reionization. This process is 
driven by the first sources of UV light in the universe and therefore can 
teach us a lot on the formation of the first stars and black holes. 
Additional information is stored into various cosmic backgrounds 
(UV, Near Infrared, X-ray) and intensity mapping (hydrogen Lyman Alpha and 
21 cm line) data. Theory is on the way to successfully interpret the wealth 
of information extracted from a number of relevant experiments but many 
questions remain that are far cry from being answered. 
I will review the recent advances and sketch promising lines for 
future research.