Joseph Judah Löb Sossnitz (Yiddish: יוסף יהודה ליב בן יחיאל מיכל זאָסניץ, romanized: Yosef Yehudah Leyb ben Yekhiel Mikhel Zosnitz; 17 September 1837 – 2 March 1910) was a Russian–American Talmudic scholar, philosopher, educator, and scientific writer.
He was granted access to the library of the city's polytechnical school, where he studied German and secular sciences.
However, due to his refusal to write against Slonimski's rival Gabriel Judah Lichtenfeld, he was dismissed from this position.
In 1888, Sossnitz relocated to Warsaw, assuming the role of editor for the scientific and Kabbalistic sections of Ha-Eshkol [he].
Among his students was Mordecai Kaplan, who credited Sossnitz as contributing to his "intellectual and spiritual development".