Abstract: In general, calculating L-2 Betti numbers of an infinite group is very complicated, while L-2 Betti numbers of a finite group is very easy. Bianchi groups are subgroups of PSL_2(C) and they are amalgamated products and HNN extensions of infinite cyclic and some finite groups( Z/2,Z/3, D_2, S_3, A_4). Biancci groups act on Mendoza complex with finite CW complex. The cohomology of Biancci groups is calculated through this action. Recently, L-2 Betti numbers of other infinite groups such as Right-angled Coxeter groups have been calculated. I hope to develop some method to calculate the L-2 Betti numbers of Biancci group. At this stage, I am still exploring. Hence, this talk is a study note as introduction to L-2 Betti numbers and Biancci groups.