Within the medieval Catholic Church, the term ‘clandestine betrothal’ was associated with the absence of witnesses, solemnities, and other formalities. Parental consent was not a legal requirement for betrothal or marriage, which was based on the free decision of the spouses. However, Martin Luther held that the will of the parties was not sufficient, because the couple was joined by God, and God’s will was reflected in parental consent. Luther intended the parents to be a public authority, and he therefore proposed a different definition of clandestine marriage that combined the absence of witnesses with the lack of parental approval. Medieval canonists had enumerated numerous types of clandestine betrothal. However, in their treatises, the jurists Johannes Schneidewin, Conrad Mauser, and Joachim von Beust translated Luther’s definition into legal terms, reducing the types of clandestine betrothal to only two. The first type, absence of witnesses, continued to be regulated by canon law, with some exceptions. The second, lack of parental approval, was governed by Roman law reinterpreted according to Scripture. Cardinal Bellarmine criticized this definition as confused, prompting the Lutheran theologians Paul Tarnov and Johann Gerhard to reply that ‘clandestine’ had acquired a new meaning: violation of the law imposing parental approval.