Over the last decade, several clusters of scientists have been using animal cells in an attempt to grow meat. Known as in vitro, or cultured, meat, the technology involves tissue engineering muscle cells for potential consumption as food. Those supporting the technology articulate a diversity of potential benefits in producing meat in this way, which include environmental-, health-, innovation-, and animal-welfare-related benefits. This essay reports on interviews with scientists and animal activists involved in making and promoting in vitro meat (IVM). While the technology remains in its infancy, its promotion has assertively been pursued with a set of promissory narratives designed to enroll potential funders, commercial investors, and consumers. The essay explores the ethical boundary-work—the drawing of boundaries around what constitutes ethical scientific practice—pursued in the creation of socio-technical expectations around IVM. In particular, it focuses on the emergence of an animal-libratory promissory narrative by exploring how ethically correct practice toward animals is constructed and used to underpin notions of what IVM is and what it can do. The key contributions of the essay are to provide a detailed analysis of the situated ethics of IVM, and to make explicit the relatedness among ethics, promise, and ontology.