This article discusses the theme of numeracy, vulnerability, ethics, and social justice. The choice of this theme highlights its relevance to the processes of teaching and learning among vulnerable youth and adults, as well as its connection to issues of ethics and social justice. The discussion has a theoretical focus, even though its development is supported by episodes extracted from empirical research conducted by the author with the Brazilian Landless Movement in her academic activity, from an ethnomathematics perspective. This perspective draws mainly from the ideas of D'Ambrosio, the philosopher Ludwig Wittgenstein in his mature period, and Michel Foucault.