The R-L4 haplogroup is a Jewish paternal lineage whose Most Recent Common Ancestor (MRCA) lived sometime around 700 CE. The vast majority of the descendants of this L4 ancestor are Jewish or have known paternal Jewish ancestry. The MRCA with the closest non-Jewish parallel branch lived about 800 BCE. L4 is a subclade of U152, which is most commonly found in present-day Italy and Switzerland.

Anyone who has tested positive for L4, or who is a Y-DNA STR match with anyone who is positive for L4 or one of its subclades (see the surname list or the FTDNA Public Haplotree for the subclades https://www.familytreedna.com/public/y-dna-haplotree/R;name=R-L4) is welcomed to join the project.