Conversion traditionally requires a three-member religious court and involves acceptance of Judaism, immersion in a ritual bath (mikve), and circumcision for males. (Reform Judaism does not always require immersion.) Already-circumcised males undergo symbolic circumcision. One also chooses a Hebrew name, to which "son (daughter) of Abraham and Sarah" is appended. Studying the basics of Judaism is a necessary precondition for conversion. In cases of doubt as to one's Jewishness, a contingent conversion can be performed (without the usual blessing). Minor children can be converted, but can opt out upon age twelve or thirteen. Rabbis often discourage conversion to Judaism, as a matter of policy, but this is not usually the case for someone who is part-Jew or married to a Jew. In some countries (Argentina, Brazil, Spain, and others), there are virtually no Orthodox conversions. Many Syrian congregations reject converts. Orthodox Jews do not necessarily recognize conversions performed under the auspices of other branches. The Israeli rabbinate (e.g. for purposes of marriage) recognizes only selected Orthodox conversions.
Jewish law does not treat apostates (Jews who have converted to another faith) as Jews. If the conversion out of Judaism was under duress, this does not apply. One who is matrilineally of Jewish descent, but was raised as a non-Jew, is to be treated as a Jew under Jewish law. From the Jewish point of view, baptism itself has absolutely no impact on one's status. Under Israel's "Law of Return," all Jews are entitled to Israeli citizenship, but this does not include those who have joined another religion.
The term "anusim" is applied to forced converts, whether of Spain, Portugal, Persia, Hungary, or elsewhere, and to their descendents. They are treated as Jews under Jewish law. However, there has been a tendency by some authorities to reject anusim who had the knowledge and opportunity to return to Judaism and declined (e.g. their wine was considered non-kosher), but this did not apply to people raised in another faith. In the past, when returning to Judaism, anusim often immersed in a mikve as part of a return ceremony, and were neither discouraged nor were they required to first study. The following special prayer was composed by Rabbi Solomon ben Simeon Duran in the fifteenth century for such an occasion:
It is rare today that Iberian anusim can prove matrilineal descent from known Jews. Furthermore, most laypersons and many rabbis are relatively ignorant of the extent to which anusim have spread throughout the world and to which crypto-Judaism has survived. Hence, Hispanics whose families are aware of Jewish descent and who wish to be accepted as part of a normative Jewish community face difficulties. Without conversion or formal return (see below), they often find themselves marginalized in the synagogue or temple, unable to marry in the synagogue, or unable to settle permanently in Israel.
Most programs for conversion to Judaism will not distinguish between returning anusim and Gentile converts. Schulamith Halevy, who researches crypto-Jewish traditions, has been advocating the reinstitution of the "return" ceremony as an alternative for anusim. This return process is akin to contingent conversion (in that it usually involves circumcision for males and immersion), with Duran's special prayer for anusim quoted above and a certificate of return ("teudah lashab ledarkhei abotav," rather than of conversion). One can also retain one's parents' names as patronymic and metronymic. Mordechai Eliahu (former Sephardic Chief Rabbi of Israel), the Chicago Rabbinical Council, and some Orthodox and Reform rabbis have adopted Halevy's procedure.
Most rabbis, of all denominations, do not allow full participation prior to return or conversion. However, in the opinion of Aaron Soloveichik--the preeminent Orthodox rabbinic authority in Chicago--and others, people who have reason to believe they are of the anusim from their mother's side, but lack proof, must be welcomed and treated as Jews in the synagogue, including being counted for prayer services, called to read the Torah, and the like, but require a return ceremony prior to marriage.
As Maimonides wrote regarding anusim in twelfth-century Spain: