Wagtails are a group of passerine birds that form the genus Motacilla in the family Motacillidae. The forest wagtail belongs to the monotypic genus Dendronanthus which is closely related to Motacilla and sometimes included therein. The common name and genus names are derived from their characteristic tail pumping behaviour. Together with the pipits and longclaws they form the family Motacillidae.
The willie wagtail (Rhipidura leucophrys) of Australia is an unrelated bird similar in coloration and shape to the Japanese wagtail. It belongs to the fantails.