The Ethnologue is a reference resource with basic information on the characteristics, classification, and geographical distribution of the world's languages.
"The purpose of the Ethnologue is to provide a comprehensive listing of the known living languages of the world. The Ethnologue is intended more as a catalog than as an encyclopedia and so provides summary data rather than more extensive descriptions of identified languages. Information comes from numerous sources and is confirmed by consulting both reliable published sources and a network of field correspondents. "--Introduction to the Web version.