The Borgarting (Old Norse: Borgarþing) was one of the four regional legislative assemblies or lawthings (lagting) of medieval Norway. Historically, it was the site of the court and assembly for the south-eastern coastal region of Norway, covering from Göta älv (now in Sweden) to the today's Risør in Agder.
The thing is named after its seat, the town of Borg (today Sarpsborg). It was established before 1164, when it absorbed the traditional districts of Grenland and Telemark. The lagting covered mostly the same areas as the current appellate court, with the addition of areas in today's Telemark, Agder, and Sweden.