Jakob Erlandsen (died 18 February 1274) was a Danish Archbishop of Lund (1254–1274) and the central character of the first great church conflict in Denmark.
King Christopher I strongly resisted the archbishop's wish of adjusting the legislation and juridical right of the Danish church with international canonical law because it meant a severe hampering of the state power, among other things of its financial energy.
After many minor conflicts, archbishop Jakob in 1256 issued the so-called Vejle Constitution, a law that was meant to secure all bishops against any kind of arrest from the king's side by threatening him with an interdict.
The arrest only partly provoked the expected interdict, but military attacks from the bishop's foreign allies and the king's sudden death weakened the royal party.
Jakob Erlandsen's career and defeat shows the great difficulties of carrying through international ecclesiastical legislation in Denmark.