Biby, Manor house in Eskilstuna Municipality, Sweden.

Biby is a former manor and säteri in Gillberga parish, 12 km southwest of Eskilstuna. Its main building is a two-storey red-painted wooden house under a säteritak (mansard-like roof), probably built in 1606 and one of Södermanland's oldest preserved wooden dwellings. It retains a Renaissance stove dated 1606. Two red outbuildings with gabled roofs flank the tree-lined drive, and behind the main house stand two loft sheds moved here from Järshammar and Västra Fyrby.

Biby is documented from the 15th century and belonged to the Stiernsköld family from the late 16th century until 1676, then to the Sparre family. Baron Gustaf Celsing bought it in 1782 and made it a fideicommiss in 1788. After the last holder, Fredrik von Celsing, died in 2008, the entail was wound up; Johan Klingspor bought the estate with about 1,200 hectares in 2013.

The estate is known since the 15th century and belonged to the Stiernsköld family until 1676, then to the Sparre family. The Celsing family, who bought Biby in 1782, served as Swedish diplomats in Turkey; their Turkish collection of paintings and documents was sold abroad after the entailed estate was dissolved and is now in Qatar.

Biby lies about twelve kilometres south-west of Eskilstuna, in Gillberga parish. The approach from the estate road is lined with an allé, and the red-painted wings with saddle roofs stand by the exit. The main building, wings, loft sheds, smithy and carpentry cottage are grouped together, so the whole yard can be seen on foot.

The Celsing family served as Swedish diplomats in Turkey, and their collection of Turkish paintings and documents was kept at Biby. After the fideicommissum was dissolved, the government declined to buy the collection, which is now in Qatar; the diplomatic archive was bought by the state.