Language learning and teaching of endangered languages have many features and needs that are quite different from the teaching of world languages. Groups whose languages are endangered try to turn language loss around; many new language teaching and learning strategies are emerging, to suit the special needs and goals of language revitalization. The teaching of "foreign languages", "majority languages", "heritage languages" and endangered languages is compared in this paper. Because of the paucity of language teaching resources for endangered languages, and especially because of the special goals of learning for language revitalization, individuals and communities and the professionals who work with them are developing novel ways of teaching and learning their ancestral language, to meet the goals of language learners and their communities. (Contains 4 notes and 1 table.)