Animals are unfortunately an afterthought in legal systems that have been developed to adjudicate the claims of humans and corporate entities. For those of us determined to extend the scope of justice to include animals, we must ask how to reshape our legal institutions to ensure that animal interests are considered alongside those of other, existing legal subjects. In this groundbreaking work, Serrin Rutledge-Prior departs from those who have proposed to extend legal personhood to animals, which in practice has proven to be exclusionary and inconsistently applied by the courts. Instead, Rutledge-Prior offers a new principle to ground legal inclusion based on a principle of multispecies legality that extends legal subjecthood to anyone – human or nonhuman – who possess interests.