A continuous mixer/reactor and a mixing process are provided in which materials flow in an orderly fashion along the length of a channel (9) and the materials are mixed in a direction transverse to the axis of the channel (9) by the provision of agitator elements (5, 7) within the channel (9) and shaking the channel (9) so that the agitator elements (5, 7) move within the channel (9) in the radial direction of the channel (9).