This chapter focuses on sign languages as natural human languages. It examines the historical and metaphysical prejudice against sign languages within a phonocentric Western tradition. The validation of signed languages has resulted in a revolution in understanding of the human language capacity, which also calls for rethinking assumptions of the nature of literature and literacy. When examined more closely, signed languages figure prominently within philosophical considerations of language, from Plato to the present. Contemporary concerns with sign language focus on their endangerment, due to biopower ideologies and institutions that seek to discourage the use of sign languages by deaf children, promoting instead the monolingual approach of oralism. In response, deaf communities have engaged in campaigns to promote linguistic human rights of deaf children to be educated in a fully accessible language, using research that points to the many cognitive gains of learning sign language for both deaf and hearing people.