Near-surface misfit dislocations can be directly observed by Scanning Tunneling Microscopy through the distortion on the positions of the atoms of the surface layer. In this way, the behavior of misfit dislocations can be followed in detail. Experiments performed in monolayer films of Cu on Ru(0001) show both climb and glide of the misfit dislocations with atomic resolution. The motion of the dislocations represents a novel pathway for surface diffusion in ultra-thin films.