We examine how Israeli Orthodox rabbis cultivate authority on reproductive medical issues, focusing on an institute of thirteen rabbis offering Halachic consultation to fertility patients affiliated with the full range of observant Judaism. The rabbis appropriate medical language and knowledge to position themselves as specialized mediators between two authoritative systems: rabbinic law and reproductive medicine. Their hybrid rabbinic-medical authority relies on continuous mapping of medical knowledge and services, networking, and collaboration with medical practitioners and rabbis of different religious sects. Rabbis negotiate Halachically appropriate (kosher) protocols of fertility treatments in line with consultees’ styles of observance, and constitute a physical presence in fertility labs. They introduce new belief systems, legal restrictions, and power relations into medical encounters. Rabbinic involvement in patients’ prenatal diagnosis emphasizes the ethical dimension of their authority: for example, they invite pregnant women facing a diagnosis of a foetal anomaly to transfer termination decisions to the rabbis. But rabbis never shoulder decisions alone, they master a procedure to divide the ethical burden and moral responsibility of post-diagnostic decisions using the network of rabbis and doctors they have cultivated to outsource and aggregate multiple medical and rabbinic opinions on each case. Rabbinic-medical authority emerges as skilful networking across authoritative systems.