在分子进化的研究中，单倍群（Haplogroup）是一组类似的单倍型（Haplotype），它们有一个共同的单核苷酸多态性祖先。因为单倍群由相似的单倍型组成，所以可以从单倍型来预测单倍群。单核苷酸多态性试验被用来确认单倍型。单倍群以字母来标记，并且以数字和一些字母来做补充，例如O3e1. Y染色体和线粒体单倍群有不同的单倍群标记方法。单倍群可用来标记数千年前的祖先来源。

在人类遗传学中，最常被拿来研究的单倍群是Y染色体（Y-DNA）单倍群和线粒体DNA（mtDNA）单倍群，这两个都可以被用来定义遗传群体。Y染色体脱氧核糖核酸单倍群仅能以父系遗传，同时mtDNA仅能以母系遗传。

A haplogroup (from the Greek:ἁπλούς, haploûs, "onefold, single, simple" and English:group), is a combination of alleles at different chromosomes regions that are closely linked and that tend to be inherited together. It is a group of individual organisms which, in terms of molecular evolution, share a common ancestor – a genetic line of descent demonstrated by a particular single nucleotide polymorphism (SNP) mutation. Because a haplogroup consists of similar haplotypes, it is usually possible to predict a haplogroup from haplotypes.