This chapter examines the regulatory framework governing the use of human embryos and gametes in treatment and research in the United Kingdom.This framework, overseen by the Human Fertilisation and Embryology Authority (HFEA), permits the use of germline genome modification in human embryos for specific research purposes, but it does not currently allow such modified embryos to be used in treatment.The chapter goes on to consider how germline genome modification may become a licensable treatment in the future, building on the recent experience of regulating research into mitochondrial donation and its clinical application in the United Kingdom.The legal and ethical challenges raised against the use of mitochondrial donation (and likely to be raised against the clinical use of germline genome modification) are also considered, including concerns arising out of EU legislation.