To make our lives easier, present societies have build large infrastructures systems which are interconnected. They provide us of energy and fuels that we need. At the same time, we have become dependent on these infrastructures. Large failures of those systems cause vary large economic and social cost to the society. The problem is that we do not quite understand why they may fail and when. Also there are powerful economic interests in maintaining our ignorance. In this talk, I will present the studies that we have carried out towards understanding the failures of the power grid. They are based on analysis of the available data from the US grids and on models constructed on the basis of those analysis. These models not only have to included the physics bases of the electric grid but also economic and social factors that condition its operation.