The Dahl surname and its variants (Soundex D400 and T400), may be found throughout Northern and Western Europe. The Dahl Surname DNA project is dedicated to using DNA and the tools of genetic genealogy to distinguish the Dahl paternal lineages.

As a surname project, the primary tool is the Y-chromosome DNA (Y-DNA) that is passed down from father to son in much the same way as Western European surnames. The Family Finder autosomal DNA test may also be used to compare two individuals who are related within six generations.