Kac-Moody groups: split and relative theories. Lattices

In this survey article, we recall some facts about split Kac-Moody groups as defined by J. Tits, describe their main properties and then propose an analogue of Borel-Tits theory for a non-split version of them. The main result is a Galois descent theorem, i.e. the persistence of a nice combinatorial structure after passing to rational points. We are also interested in the geometric point of view, namely the production of new buildings admitting (nonuniform) lattices.