According to Agrippa's trilemma, an attempt to justify something leads to either infinite regress, circularity, or dogmatism. This essay examines whether and to what extent the trilemma applies to ethics. There are various responses to the trilemma, such as foundationalism, coherentism, contextualism, infinitism, and German idealism. Examining those responses, the essay shows that the trilemma applies at least to rational justification of contentful moral beliefs. This means that rationalist ethics based on any contentful moral belief are rationally unjustifiable.