In the Earth's crust, a large part of the deformation is located at the level of fault zones. The study of faults represents a major societal challenge, both from the point of view of understanding the seismic risk, and for the mitigation of industrial risk in geoengineering (storage in geological environment or for energy production via geothermal energy). The mechanical behavior of fault gouge and adjacent wall rock is a key in understanding faulting. It is still unclear how and where does localization occur, and what are the respective roles of the damaged and intact rocks. The effect of the stress state on the rheology and on the seismic behavior, both in the damaged zone and in the fault core, is still unknown. One way to address these questions is to perform laboratory experiments in order to understand the relevant physical mechanisms. In my presentation I will show results from different types of experiment, from uniaxial tests with deformation measurements via digital image correlation (DIC) to triaxial tests with acoustic emission monitoring and aiming at unraveling field scale phenomenon.