Estrid Svendsdatter of Denmark (Estrith, Astrith: 990/997 – 1057/1073), was a Danish princess and titular queen, a Russian princess and, possibly, duchess of Normandy by marriage. She was the daughter of Sweyn Forkbeard and perhaps Gunhild of Wenden and half-sister of Cnut the Great. By Ulf Jarl, she was the mother of the later King Sweyn II Estridson and Beorn Estrithson. The dynasty that ruled Denmark in 1047–1412 was named after her. Though never a ruler or wife of a king, she was known in Denmark as queen during her son's reign.
According to other researchers Estrid was the daughter of Sweyn Forkbeard and Sigrid the Haughty, herself the daughter of Skagul Toste, making Olof Skötkonung, the son of Sigrid the Haughty and Eric the Victorious, Estrid's half-brother while Canute the Great, Harald and Świętosława her other half-siblings, as children of Sweyn Forkbeard and the Polish princess Gunhild, daughter of Mieszko I of Poland.