Rabbi Yisrael Meir Kagan wrote two major halakhic works on the evil tongue: Chafetz Chaim ("Desirer of Life") and Shmirat HaLashon ("Guarding the tongue"), both 1873. The Chafetz Chaim lists 31 speech-related commandments mentioned in the Torah. An English translation, Guard Your Tongue, (2002) anthologizes the teachings of these two books.
Read more about this topic: Lashon Hara