In the 12th century, notarial documents in Upper and Central Italy achieved the status of fides (publica/maxima, plena or plenissima). The study proceeds from the observation that this term implied not only 'internal evidence'/'probatory force' but also 'faith'/'trust' and 'credibility'. With reference to the standing of individual notaries, the deposition of documents, the choice of location and witnesses, and intervention on the part of local urban governments, it goes on to trace the formation of trust in documentary procedures, the factors this trust was based on, and the processes of change it underwent.