Rabbi Isaac ben Jacob or Yitzhak ben Yaakov, nicknamed "ha-Lavan" or "the white" was a 12th-century rabbi of Bohemia.
He was a Tosafist and liturgical poet who flourished at Prague in the late 12th century.
He was among the earliest of the tosafists ("ba'ale tosafot yeshanim"), a contemporary of Rabbi Eleazar of Metz, and a pupil of Rabbenu Tam.
739, quotes Isaac ben Jacob's commentary on Ketubot, a manuscript of which exists in the Munich Library (No.
He is also mentioned in a commentary to the Pentateuch written in the first half of the 13th century.