With some 108 independent genealogical units, South America is the linguistically most diverse region of our planet and presents a particular challenge to linguists seeking to understand the genealogical relationships among human languages. Recent years have seen a resurgence of interest in the internal classification of South American language families, and this article provides a critical overview of research in this very active area, focusing on the seven largest language families of the continent: Arawakan, Cariban, Jê, Panoan, Quechuan, Tukanoan, and Tupian. The strengths and weaknesses of major classification proposals are examined, and directions for future research discussed. Several long-distance relationship proposals that South Americanists are actively debating, including Tupi-Cariban, Pano-Takanan, Quechumaran, TuKaJê, and Macro-Jê, are also examined.