We analyze multiwavelength observations of the cancellation of a moving magnetic feature and a plage element at the outer edge of the moat of an isolated, round sunspot. The event lasted for some 35 minutes until the smaller flux concentration disappeared completely from the photosphere. The data set consists of high-resolution, full vector spectropolarimetric measurements of four visible lines and two near-infrared lines, along with speckle-reconstructed G-band and Ca II H filtergrams. The observations reveal strong chromospheric emission at the neutral line separating the two magnetic poles; it becomes visible 18 minutes after the cancellation has started and persists for 25 minutes. We have carried out an inversion of the observed Stokes profiles to determine the variation of the vector magnetic field, temperature, and line-of-sight velocity during the cancellation. No significant changes in field strength, field inclination, or temperature are observed in either of the two opposite-polarity patches. The decrease in magnetic flux is primarily due to a decrease in magnetic filling factor, which is accompanied by strong upflows (of at least 1.1 km s-1) in the smaller flux concentration. These results suggest that the cancellation is due to magnetic reconnection in the photosphere.