Haplogroup I (M170) is a Y-chromosome DNA haplogroup. It is a subgroup of haplogroup IJ, which itself is a derivative of the haplogroup IJK. Subclades I1 and I2 can be found in most present-day European populations, with peaks in some Northern European and Southeastern European countries.

In human genetics, a human Y-chromosome DNA haplogroup is a haplogroup defined by mutations in the non-recombining portions of DNA from the male-specific Y chromosome. Many people within a haplogroup share similar numbers of short tandem repeats (STRs) and types of mutations called single-nucleotide polymorphisms (SNPs).