Surface plasmons are electrical charge oscilllations that can be excited on a metal surface by light. They provide a means by which optical energy can be converted into electrical energy and manipulated at the nanoscale. Surface plasmons can propagate as waves in waveguide devices and can exists as localised resonances in metal nanoparticles. Plasmonic circuits have been developed that mimic waveguide-based optical circuit devices, and plasmons in metal nanoparticles have been likened to excitations in electrical circuits. Although surface plasmons are electrical in nature, they preserve phase coherence with the incident optical fields that excite them. In this regard surface plasmon devices represent a convergence between optics and electronics. In this paper I review some of the work in these two fields and discuss their progress towards devices for the nanoscale control of optical signals and optical signal processing.