Bar Mitzvah means Son of the Commandment and Bat Mitzvah means Daughter of the Commandment. When a Jewish child reaches the age of 13 (12 for Orthodox girls), according to Jewish law he/she becomes an adult and assumes responsibility to observe the Mitzvot (commandments) as an independent individual. An early reference to the Bar Mitzvah is found in the Ethics of the Fathers (chapter 5, verse 25) '...a thirteen-year-old becomes obliged to observe the commandments'.
At this stage the young person can be included in a minyan, a quorum of ten Jewish adults (all male in the case of the Orthodox community) required to form a congregation for communal prayer.
In the Bar/Bat Mitzvah ceremony the child affirms his or her readiness through the Bar/Bat Mitzvah rituals: reciting Blessings, reading the Torah portion and Haftarah, and in some communities delivering a sermon on the reading or leading part of the synagogue service. How much or little is done for a Bar/Bat Mitzvah is not as important as the taking part and embracing the Jewish religion. The minimum required for a Bar/Bat Mitzvah is to recite the Blessings before and after the reading of a portion from the Torah, but more may be done according to ability.
The Bar/Bat Mitzvah ceremony is a fairly modern development in Judaism, being first recorded some six hundred years ago. On the first Shabbat (Saturday) after a child's thirteenth birthday he/she is called to read from the Torah in the synagogue, although the Bar/Bat Mitzvah may also take place on a Monday or a Thursday.
The Bat Mitzvah is a very recent innovation in Judaism. In the non-Orthodox community the Bat Mitzvah girl will do exactly the same as the boys in her synagogue. However, the Orthodox community does not, in general, allow girls to read directly from the Torah. Instead B'nai Mitzvot girls will study together and make a group presentation to the congregation in a special service.