The quantum phase transition between the global phase coherent state and infinite conductivity to the localized states with negligible conductivity has attracted the attention of physicists for decades. Recent years brought forward a wealth of dramatic results, such as simple activated temperature dependence of the resistance and little parks oscillations in the insulating phase, a large peak in the magnetoresistance, peculiar I-V characteristics and a pseudogap in the tunneling density of state above the critical temperature. Our group contributes to the understanding of these phenomena in several different approaches. We have utilized macroscopic tunnel junctions to probe the density of states and found a similar superconducting energy gap from both side of the SIT. We have further shown that the superconducting energy gap survive also across the magneto resistance peak. In our efforts to detect the evolution of the superconducting energy gap we have also utilized a new technique to the field of disordered superconductors, namely THz optical spectroscopy. In this experiment we measured two optical parameters: the transmission and phase shift of THz radiation traversing through the studied films. This approach enables us to extract the complex response function.