Circumcision
Circumcision is very important to most branches of Judaism, with over 90% of male adherents having the procedure performed as a religious obligation. The basis for its observance is found in the Torah of the Hebrew Bible, in Genesis chapter 17, in which a covenant of circumcision is made with Abraham and his descendants. Jewish circumcision is part of the "brit milah" ritual, to be performed by a specialist ritual circumciser, a "mohel", on the eighth day of a newborn son's life, with certain exceptions for poor health. Jewish law requires that the circumcision leaves the glans bare when the penis is flaccid. Converts to Conservative and Orthodox Judaism must also be circumcised; those who are already circumcised undergo a symbolic circumcision ritual. Circumcision is not required by Judaism for one to be considered Jewish, but some adherents foresee serious negative spiritual consequences if it is neglected.
Conversion to Judaism
In general, immersion in the mikveh is an important part of a traditional conversion. If the person who is converting is male, circumcision is a part of the traditional conversion process as well. If the male who is converting has already been circumcised, then a ritual removal of a single drop of blood will take place ("hatafat dam brit"). However, more liberal branches of Judaism have a more relaxed requirement of immersion and circumcision.