All-optical switching and routing of light in fibers and waveguides has the potential of handling optical signals at ul rahigh speed. By using very rapid electronic nonlinearities in transparent materials, extremely fast switching free of thermal problems could be obtained. The guided wave environment reduces the peak power requirements. Although the transit times may be long, these devices operate in a "pipeline" scheme, allowing very fast rates. A number of nonlinear devices have been considered for all-optical switching, including nonlinear directional couplers, Mach-Zehnder interferometers and mode-splitters. We will review these in the first part of the talk.