The Beit Din
The Jewish court of law.
The Torah commands us to "appoint judges and officials for your tribes" (Deuteronomy 16:18).
Throughout history Jews have observed this commandment by setting up various ways of adjudicating Jewish legal disputes.
During the time of the Temple in Jerusalem, the Sanhedrin, a group of 71 rabbis, heard cases and handed down rulings to the Jews of Israel. Soon after the destruction of the Temple, when Jews began spreading throughout the diaspora, gathering 71 legal authorities was no longer practical. Instead, consulting a beit din (sometimes spelled bet din, or beth din, plural batei din), a group of three men knowledgeable in Jewish law, eventually became the commonly accepted way for Jews to address legal disputes. These three men work together to come to a ruling according to halakhah (Jewish law). During the time of the Sanhedrin, this option had only been available to those living in small towns.
In Israel today, batei din are a part of the formal legal system, and must be consulted for some ritual matters (such as divorces and conversions). Members of Israeli batei din are called dayanim (singular: dayan, meaning decider) and many have been through rigorous training programs focused on settling disputes and making legal rulings. Outside of Israel there are some national and local batei din, such as the Beth Din of America, or the Beth Din of Manchester, that are available for those who want to employ their services. These batei din are typically staffed by rabbis, and those on the Beit Din of America are often also lawyers.
However, according to Jewish law, all one needs for a beit din is three Jewish men, so technically you could create your own without using one of the formal organizations. Often the proceedings of a beit din are held in a synagogue, but they can actually take place anywhere, even at home or at the park.
There are many situations in which a Jew might consult a beit din, but the most common is to arrange a get, or a Jewish divorce document. In order for a couple to be divorced according to Jewish law, the man must present the woman with a get in front of a beit din. The beit din is present to ensure that everything is done precisely according to Jewish law and is thus valid (at least one member of a beit din for a get is usually an expert on gittin, the laws of Jewish divorce). A beit din may also be involved in property division, custody, and visitation issues that arise from a divorce.