The authors publish a previously unedited Regimen of Health attributed to Avenzoar (Ibn Zuhr), translated at Montpellier in 1299 in a collaboration between a Jewish philosopher and a Christian surgeon, the former translating the original Arabic into their shared Occitan vernacular, the latter translating that into Latin. They use manuscript evidence to argue that the text was produced in two stages, first a quite literal version, then a revision improved in style and in language adapted to contemporary European medicine. Such collaborative translations are well known, but the revelation of the inner workings of the translation process in this case is exceptional. A separate Hebrew translation by the philosopher (also edited here) gives independent evidence of the lost Arabic original.