One objective of the Catalogue of Endangered Languages (ELCat) was to produce new knowledge. This chapter explores discoveries from ELCat that have resulted in new knowledge about the world's languages. The Catalogue of Endangered Languages contains massive amounts of new information on 3,394 endangered languages. It records information on each language's location, numbers of speakers, degree of endangerment, classification, alternate names, major variants, resources about the language. ELCat has provided clear empirical confirmation of the commonly repeated claim that languages are becoming extinct at a highly accelerated rate. There are a good number of unclassified languages whose genetic affiliation is unknown. Many of these are long extinct languages that are too poorly attested to be grouped with any other language or language family. The Catalogue of Endangered Languages indeed has provided new knowledge, knowledge that allows us now to know things that were previously unknown, new "known knowns."