Fluidic mixing is the process of mixing at least two liquids. It plays a very important role in many fields, including high-throughput synthesis, analytical chemistry, and microbiological analysis systems. In a microfluidic system, fluidic mixing is difficult because the scale of the channel generates laminar flow. The liquid is thus mixed only by molecular diffusion, which is too slow for many applications. In recent years, several mechanisms have been proposed and patented to improve microfluidic mixing efficiency. This paper reviews five kinds of active micromixer and four kinds of passive micromixer and then discusses their advantages.