Haplogroups are groupings of genetic markers that imply common ancestry hundreds or thousands of years ago. They are based on a hierarchical tree and assigned letters and contain subgroups referred to as sub-clades. Haplogroups are only associated with mtDNA and Y SNP & Y-STR testing.

A haplogroup is a genetic population who share a common ancestor on the paternal or maternal line. Haplogroups are assigned letters of the alphabet, and refinements consist of additional number and letter combinations.