William Lyndwood was bishop of St. David's in Wales; Keeper of the Privy Seal; advisor on ecclesiastical law to the Archbishop of Canterbury; and also a skilled diplomat and negotiator for the king. However impressive these credentials may be, his name is remembered because of his Proviniciale, the principal authority on English canon law.
The main body of canon law, in England and everywhere, was the Corpus iuris canonici, the law of the Roman Catholic church. The law of the church allowed for provincial legislation and local custom, as long as these were reasonable and not repugnant to the Corpus iuris canonici. Lyndwood's work is a compilation of the provincial laws of England and his gloss was accepted as authority throughout Christendom.
Lyndwood's text was completed in 1434 and was first printed in 1483—one of the first law books printed in England.