The Jewish circumcision ceremony, brit mila, is enacted by a trained specialist called a mohel.
[1] The first pages of a mohel book are typically dedicated to the special prayers recited during brit mila.
Today, the entries are usually digital, and efforts are being made to digitalise existing mohel books as well.
However, these books often remained in private hands, making them hard to access for scholars and families doing genealogical research.
[1] Mohel books in combination with cemeteries and place names can give an overview of the movement of Jews in Europe in the Middle Ages and later centuries.