Halsten Stenkilsson, English exonym: Alstan (Old Icelandic: Hallstein) was a king of Sweden, son of King Stenkil and a Swedish princess. He became king after his father Stenkil's death (1066), and he may have ruled together with his brother Inge the Elder. The date of his death is not known.
Little is known of his time as king. In a scholia in the work of Adam of Bremen, he is reported to have been elected king after the death of two pretenders, but deposed after a short while. That he ruled together with his brother Inge has some support from a papal letter from 1081, by Pope Gregory VII, which refers to two kings with the initials A and I, and where they are called kings of Västergötland (rege wisigothorum). However, the king "A" could also be Håkan the Red. His co-rulership with his brother Inge is also mentioned in the Hervarar saga.
In the regnal list of the Westrogothic law, he is said to have been courteous and cheerful, and whenever a case was submitted to him, he judged fairly, and this was why Sweden mourned his death. He was the father of the co-rulers Philip and Inge the Younger.