In human genetics, Y Haplogroup E1b1b (E-M215), previously known as E3b, is a major Y-chromosome haplogroup, which is a division of the macro haplogroup E, and which is defined by the single nucleotide polymorphism (SNP) mutation M215. In other words it is one of the major paternal lines of humanity, linking from father-to-son back to a common male-line ancestor. It is a subject of discussion and study in genetics as well as genetic genealogy, archaeology, and historical linguistics.

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E1b1b and E1b1b1 are the currently accepted names found in the proposals of the Y Chromosome Consortium (YCC), for the clades defined by mutation M215 and M35.1 respectively, which can also be referred to as E-M215 and E-M35.1. The nomenclature E3b (E-M215) and E3b1 (E-M35.1) respectively were the YCC defined names used to designate the same haplogroups in older literature with E-M35.1 branching as a separate subclade of E-M215 in 2004. Prior to 2002 these haplogroups were not designated in a consistent way, and nor was their relationship to other related clades within haplogroup E and haplogroup DE. But in non-standard or older terminologies, E1b1b is for example approximately the same as "haplotype V", still used in publications such as Gérard et al. (2006).