It is well known that the Tianzhu shiyi (first published 1603) is the development of a previous catechism published some twenty years before, which Matteo Ricci completely remodeled according to his discussions with Chinese intellectuals. This article shows that Ricci’s mentor, Alessandro Valignano, and particularly his Catechismus japonensis, written in Japan from 1579 to 1582, shaped Ricci’s methods and ideas. This overlooked connection between the two works enables us to understand better Ricci’s debt toward his predecessor and his breakthrough in terms of engagement with indigenous culture.