Saul and the Witch of Endor by Jacob Van Oostsanen, 1 Samuel 28, Bible.Gallery

Jacob Cornelisz van Oostsanen (before 1470 – 1533) was a Northern Netherlandish designer of woodcuts and painter. He was one of the first important artists working in Amsterdam, at a time when it was a flourishing provincial town.

Little is known about Jacob Cornelisz van Oostsanen's life. Historians rely mostly on the biographical sketch of him written by Karel van Mander, the archives of Amsterdam, and the archives of Egmond Abbey, a Benedictine monastery that commissioned works by him. His name indicates he was from Oostzaan, North Holland, east of the river Zaan, north of Amsterdam. His family managed land in that area. A good impression of life there in those times can be had by a visit to the Zaanse Schans. His entire family were painters. Cornelis Buys I, also known as Master of Alkmaar, was his brother, as was Cornelis Buys II. His sons Cornelis Jacobz and Dirk Jacobsz became portrait painters, as did his grandsons Cornelis Anthonisz and Jacob Dirksz.

As birth or baptism dates have been lost, all of their birth dates have been approximated from other archival evidence such as death dates of other family members. Similar to the archival evidence surrounding Frans Hals, the first known commissions for Jacob Cornelisz were from when he was at least 35 years of age. It is assumed that he worked in a painters's workshop before that, and judging from his close copies of Haarlem painting techniques, this was possibly in Haarlem.

He bought his first house in Amsterdam in 1500, in the Kalverstraat. Twenty years later he bought the neighboring house. For this reason he is sometimes called Jacob Cornelisz van Amsterdam. His wife is called a widow in archives for the first time in 1533. The last payments made to him according to the Egmond Abbey archives were in 1526–1528 for a retable (lost during the troubles of the Protestant Reformation).