Horizontal Gene transfer (HGT), also Lateral Gene transfer (LGT), is any process in which an organism incorporates genetic material from another organism without being the offspring of that organism. By contrast, vertical transfer occurs when an organism receives genetic material from its ancestor, e.g. its parent or a species from which it evolved. Most thinking in genetics has focused on the more prevalent vertical transfer, but there is a recent awareness that horizontal Gene transfer is a significant phenomenon. Artificial horizontal Gene transfer is a form of genetic engineering.

• History of horizontal gene transfer
• Viruses of horizontal gene transfer
• Prokaryotes of horizontal gene transfer
• Eukaryotes of horizontal gene transfer
• Evolutionary theory of horizontal gene transfer
• See also of horizontal gene transfer
• Sources and notes of horizontal gene transfer
• Further reading of horizontal gene transfer