Rabbi Menachem Mendel Krengel was a Polish author and bibliographer from the city of Krakow. His main contribution to Jewish scholarship was his revised edition of Chaim Yosef David Azulai’s bibliographical work, Shem HaGedolim. Krengel added a biography of the author (known as the Chida), a bibliography of the Chida’s works, extensive annotations, and additional names of authors from Krakow that the Chida had omitted from Shem HaGedolim. Krengel was also involved in an extended controversy with Krakow’s rabbi over the eruv in Krakow, and published a work on the matter entitled “Torat Eruvin.”