This paper is on the metaphysics and normativity of Jewish identity. It starts with a metaphysical question: “Can a Jewish person become non-Jewish?” This question and the related question “What is Jewishness?” are both ambiguous, because the word “Jewish” is ambiguous. The paper outlines five concepts of Jewishness: halachic, religious, ethnic, and cultural Jewishness, as well as being Jewish in the sense of belonging to the Jewish community. In some of these senses of “Jewish” a Jewish person is always Jewish. (...) In other senses a Jewish person can become non-Jewish. The paper closes with a normative question: Should a person who is Jewish, in the sense of belonging to the Jewish community, become non-Jewish? The paper explains reasons for and against staying in the Jewish community and in doing so highlights a tension, rather than telling anyone how they should identify. (shrink)