Abstract: The state of the art of active olfaction(also called mobile robot odor localization) is reviewed in detail.The principles of typical odor/gas sensors and wind-direction sensors used in active olfaction are analyzed.The three main steps included in the active olfaction,i.e.,plume finding,plume tracking and odor/gas source declaration,and the associated strategies applied to each step are summarized.The difficulties of active olfaction are pointed out at the end.