Around 11000 years ago the first domesticated mammals emerged in the Fertile Crescent.Over time, these animals spread to fertile regions both to the east and west of their domesticcentre of origin. By 6000 BP, animal husbandry had reached Northern Europe, and it hadbecome established in Norway by circa 4100 BP. Domestic sheep (Ovis aries) was probablyamong the first domestic species to be introduced to Norway and by the Middle Ages (476-1453 AD) animal husbandry and sheep herding was well established here. Not much is knownabout the composition of domestic sheep in mediaeval Norway, but it has been suggested thatnew breeds were introduced from other countries as this was a time of increasing trade.Four different mitochondrial DNA (mtDNA) haplogroups, known as A, B, C and D,have been observed in domestic sheep, of which mtDNA haplogroup A and B are found inEurope. In this study I analysed genetic data obtained from sheep bones excavated fromarchaeological sites (Oslo, Bergen and Trondheim) in Norway dated to the Middle Ages (476-1453 AD). I also included a bone sample dated to the Viking Age (800-1066 AD) to see if anygenetic variation could be obtained from an older sample. I implemented methods forextracting ancient mtDNA from bones, and aimed to produce reliable extracts that could beauthenticated as mediaeval sheep DNA. Authentic mtDNA sequences of mediaeval domesticsheep could provide information that would help answer questions regarding the tradinghistory and composition of breeds at different geographical regions in mediaeval Norway.Sheep extracts were amplified with sheep specific primers and cytochrome b primerssimultaneously. Negative and positive controls, as well as samples of different species wereincluded in the amplifications. PCR amplifications visualised on electrophoresis agarose gelscould exclude human and cross-contamination of sheep by the nature of the controls. Thissuggested that the genetic data were authentic. Of 70 domestic sheep samples, 16 weresuccessfully sequenced, including one from the Viking Age. Two mtDNA haplogroups wereobserved: A and B. One specimen from Trondheim was allocated to haplogroup A, whereasthe remaining samples were haplogroup B. The 16 sequences used in the phylogeneticanalyses were short (88 bp), and thus not informative enough to settle questions regarding thetrade and composition of breeds in mediaeval Norway. However, it could be concluded thatthe sheep sequences were authentic, and that two mtDNA sheep lineages were present inNorway in the Middle Ages.