The white wagtail is a small passerine bird in the family Motacillidae, which also includes pipits and longclaws. The species breeds in much of Europe and the Asian Palearctic and parts of North Africa. It has a toehold in Alaska as a scarce breeder. It is resident in the mildest parts of its range, but otherwise migrates to Africa. In Ireland and Great Britain, the darker subspecies, the pied wagtail or water wagtail predominates; this is also called in Ireland willie wagtail, not to be confused with the Australian species Rhipidura leucophrys which bears the same common name. In total, there are between 9 and 11 subspecies of M. alba.

The wagtails, longclaws, and pipits are a family, Motacillidae, of small passerine birds with medium to long tails. Around 70 species occur in five genera. The longclaws are entirely restricted to the Afrotropics, and the wagtails are predominantly found in Europe, Africa, and Asia, with two species migrating and breeding in Alaska. The pipits have the most cosmopolitan distribution, being found mostly in the Old World, but occurring also in the Americas and oceanic islands such as New Zealand and the Falklands. Two African species, the yellow-breasted pipit and Sharpe's longclaw, are sometimes placed in a separate seventh genus, Hemimacronyx, which is closely related to the longclaws.