Ranulf de Glanvill was Chief Justiciar of England during the reign of King Henry II (1154–89) and was the probable author of Tractatus de legibus et consuetudinibus regni Anglie, the earliest treatise on the laws of England.

The Tractatus de legibus et consuetudinibus regni Angliae, often called Glanvill, is the earliest treatise on English law. Attributed to Ranulf de Glanvill and dated 1187–1189, it was revolutionary in its systematic codification that defined legal process and introduced writs, innovations that have survived to the present day. It is considered a book of authority in English common law.