We present series of experiments conducted on model systems consisting of smooth solid surfaces covered with end grafted polymer chains at controlled surface density, and put into contact with either it polymer melt or it crosslinked elastomer of the same chemical species, and devoted to the characterization of friction as a function of the molecular parameters of the interface. Two techniques were used to do so: Near-Field Laser Velocimetry. which allows us to directly measure the local velocity at the interface when the melt is sheared against the grafted surface, and friction force measurements in it JKR like apparatus in the case of elastomers. Results will be discussed in the framework of molecular models of chain interdigitation and chain pull-out mechanisms.