This chapter addresses the practical matters of identifying and revitalizing or reviving endangered languages. The chapter will explore, in turn, the means by which one might determine that a language is endangered and evaluate the severity of its endangerment, the possible goals that one might have in attempting to preserve and revitalize it, the question of how to determine which variety of an endangered language merits rehabilitation, and the means and methods by which one might attempt to do this. The chapter will also describe and discuss two instances of such efforts, that of Welsh and that of Modern (Israeli) Hebrew.