The genetic history of the British Isles is the subject of research within the larger field of human population genetics. It has developed in parallel with DNA testing technologies capable of identifying genetic similarities and differences between both modern and ancient populations. The conclusions of population genetics regarding the British Isles in turn draw upon and contribute to the larger field of understanding the history of the human occupation of the area, complementing work in linguistics, archaeology, history and genealogy.
Research concerning the most important routes of migration into the British Isles is the subject of debate. Apart from the most obvious route across the narrowest point of the English Channel into Kent, other routes may have been important over the millennia, including a land bridge in the Mesolithic period, as well as maritime connections along the Atlantic coasts.
The periods of the most important migrations are contested. The Neolithic introduction of farming technologies from mainland Europe is frequently proposed as a period of major change in the British Isles. Such technology could either have been learned by locals from a small number of immigrants or have been introduced by colonists who significantly changed the population.
Other potentially important historical periods of migration that have been subject to consideration in this field include the introduction of Celtic languages and technologies (during the Bronze and Iron Ages), the Roman era, the period of early Germanic influx, the Viking era, the Norman invasion of 1066, and the era of the European wars of religion.