Joel was a political and legal philosopher. He is known for his work in the fields of ethics, action theory, philosophy of law, and political philosophy as well as individual rights and the authority of the state. Feinberg is seen as one of the most influential figures in American jurisprudence.
He proposed an interest-based approach to non-human animal rights that saw interests as requiring mental states (hence sentience), implying a sentiocentric moral scope. He was an atheist and had a naturalistic worldview. He said "Conceptual clarity is neither more or less important for public policy than factual discovery. Each is vitally necessary and the two are mutually dependent."