One of the most interesting features discovered by Chandra satellite observations of galaxy clusters are the sharp X-ray surface brightness discontinuities, accompanied by jumps in gas temperature named “cold fronts”. They are not shock fronts in that the temperature and density jumps conspire to maintain the gas pressure continuous across the front. Originally thought of being the result of subsonic (transonic) motions of head-on merging substructures with suppressed thermal conduction, now it is clear that they have to be generated by various mechanisms. This conclusion is in great part due to the discovery of (multiple) cold fronts in well-behaved, apparently relaxed clusters. I will discuss the different mechanisms such as oscillation of the cD and the low entropy gas, hydrodynamic gas sloshing, dark matter peak oscillation (due to scattering of a smaller dark matter systems) and the impact of these mechanisms on the dynamics of the intracluster gas in light of new Chandra and XMM observations.