This monograph is a compilation of original and recent research on southern South American stag beetles (Coleoptera: Scarabaeoidea: Lucanidae). In the study area, the wholly endemic stag beetle fauna includes 31 species in three subfamilies. A key to genera of southern South American Lucanidae is provided. Updated information on genera that have been recently revised is included. All species are redescribed and keys are provided in English and Spanish when appropriate.