Ludwig Herzer, born Ludwig Herzl, (born 18 March 1872 in Vienna, Austria-Hungary, died 17 April 1939 in St. Gallen, Switzerland) was an Austrian physician and librettist.

There he studied medicine at the University of Vienna and worked as a gynecologist as his main profession.

He also wrote operetta librettos, often in collaboration with other well-known librettists such as Alfred Grünwald or Fritz Löhner, for Edmund Eysler, Franz Lehár and Robert Stolz, among others.

After the annexation of Austria by Nazi Germany, he was forced to flee as a Jew.

With great difficulty he was able to reach Swiss territory near Hohenems-Diepoldsau on 29 November 1938.