Rabbinic law asks a would be convert to Judaism to be turned away three times before instruction begins, a custom explained as testing sincerity in a tradition that does not proselytise and that has, across long stretches of history, made conversion actively dangerous under regimes hostile to Jewish practice. Once accepted as a serious candidate, the convert undertakes a substantial course of study covering Jewish law, practice, history and belief, its length and content varying by community and by the sponsoring rabbi or beit din, the rabbinic court of three that ultimately judges the conversion valid.
The classical requirements converge on a beit din's acceptance of the candidate's sincerity and knowledge, immersion in a mikveh, a ritual bath meeting exacting standards of construction and natural water source, and, for men, circumcision, or, for men already circumcised, a symbolic drawing of a drop of blood, hatafat dam brit, understood to complete the covenant physically as well as spiritually. Because Judaism has no single central authority, what counts as a valid conversion is itself a matter of real and consequential disagreement between Orthodox, Conservative and Reform authorities, and a conversion recognised by one movement is not automatically recognised by another, a division with direct legal consequences in Israel, where recognised Jewish status affects immigration and marriage rights.