Some features of the collisional properties of Rydberg atoms are demonstrated by some recent examples. The collisional cross-sections mainly depend on two parameters : the energy defect between the considered level and the closest hydrogenic states, and the interaction between the quasi-free Rydberg electron and the perturber. Moreover it is shown that the inelastic processes can contribute to the broadening of the optical Rydberg lines. In the presence of a DC electric field new effects can arise, as demonstrated by some recent experiments.