Orthodox Judaism is the stream of Judaism that adheres to a relatively strict interpretation and application of the laws and ethics first canonized in the Mishnah (the Oral Law) and subsequently developed and applied by the later authorities known as the Gaonim, Rishonim, and Acharonim.
Compared to other modern Judaisms, Orthodox Judaism is characterized by:
- Belief that the Torah was transmitted by God to Moses;
- Belief in a Jewish eschatology, including a messiah, a rebuilt Temple in Jerusalem, and the resurrection of the dead.
- Adherence to Halacha, traditional Jewish law, as interpreted and determined by Orthodox rabbis; and
- Intensive dedication to the study of Torah, as a matter of practice, belief, and organizational priority.
Diversity within Orthodox Judaism
Orthodox Judaism's central belief is that the Torah, including both the Written Law and the Oral Law, was given directly from God to Moses. As a result, Orthodoxy expects all Jews to live in accordance with the Torah as explicated by Jewish law.
However, since there is no one unifying Orthodox body, there is no one official statement of Jewish principles of faith and no single interpretation of Jewish law. Rather, diverse Orthodox groups claim to be non-exclusive heirs to the received tradition of Jewish belief and law.
Orthodox groups vary in their social structures, cultural practices, religiosity, relation to secular and non-Orthodox Jewish culture, and specific understandings of Jewish law. These groups fall into several overarching, informal categories: Modern Orthodox Judaism and Haredi Judaism, the latter comprising Hasidic Judaism and "Mitnagdish" (non-Hasidic Haredi) Judaism. Orthodoxy also is segmented, in effect, along ethnic lines between Ashkenazi, Sephardi and other Jewish ethnicities.
- Modern Orthodoxy advocates increased integration with non-Jewish society, regards secular knowledge as inherently valuable, and is somewhat more willing to use Talmudic arguments to revisit questions of Jewish law
- Religious Zionism, characterized by belief in the importance of the modern state of Israel to Judaism, often intersects with Modern Orthodoxy.
- Haredi Judaism advocates segregation from non-Jewish culture, although not from non-Jewish society entirely. It is characterized by its focus on community-wide Torah study (in contrast with Modern Orthodoxy, which decentralizes the role of Torah study for lay people. Engaging in the commercial world is often seen as a legitimate means to achieving a livelihood, but participation in modern society is not perceived as an inherently worthy ambition. The same outlook is applied with regard to obtaining degrees necessary to enter one's intended profession: where tolerated in the Haredi society, attending secular institutions of higher education is viewed as a necessary but inferior activity. Pure academic interest is instead directed toward the religious edification found in the yeshiva.
- Hasidic Judaism places great emphasis on all the preservation of the Jewish traditions of its roots, including the mystical teachings of the Kabbalah. Those roots reach to eastern and central European Orthodox Jewish groups of the mid- 18th century. As with some modern Christian groups, such as the Amish, there has been relative or complete social isolation of Hassidic Jews from secular society and from other religious Jews, including modern Orthodox Jews. Many features of daily dress have been conserved intact from previous centuries among Hasidim, and these traditional styles are usual among men. There are numerous very distinct groups within the Hasidic world, and these differ according to adherence to particular Rabbinical teachings, culture and social network. One of these groups, the Chabad-Lubavitcher sect, proselytizes within Jewish born people of any belief, and among secular, agnostic, and atheist Jews.
Orthodox movements, organizations and groups
Modern Orthodox Judaism constitutes a large segment of Orthodoxy in America, Canada and England. Modern Orthodoxy is represented largely by the Union of Orthodox Jewish Congregations of America, more commonly known as the Orthodox Union or OU, and the Rabbinical Council of America or RCA.
The National Council of Young Israel, and the Council of Young Israel Rabbis are smaller groups that were originally founded as Modern Orthodox organizations. These groups are more fervently Zionistic and considered more right wing in their orientation (e.g., allied with the settlement movement in Israel). Israeli government leaders typically refuse to deal with the NCYI, preferring to work with the more mainstream Orthodox Union.
The Chief Rabbinate of Israel was originally founded with the intention of representing all of Judaism within the State of Israel, and has two chief rabbis: One is Ashkenazic (of the East European and Russian Jewish tradition) and one is Sephardic (of the Spanish, North African and middle-eastern Jewish tradition). The rabbinate has never been accepted by most Haredi groups located in the Land of Israel. Since the 1960s the Chief Rabbinate of Israel has moved somewhat closer to the positions of Haredi Judaism. Chief Rabbinate of Israel
Agudath Israel of America (also: Agudat Yisrael or Agudas Yisroel) is a large and influential Haredi group in America. Its roots go back to the establishment of the original founding of the Agudath Israel movement in 1912 in Kattowitz (Katowice), Germany (now Poland). The American Agudath Israel was founded in 1939. There is an Agudat Israel (Hasidic) in Israel, and also Degel HaTorah (non-Hasidic "Lithuanian"), as well as an Agudath Israel of Europe in Europe. These groups are loosely affiliated through the World Agudath Israel, which from time to time holds a major gathering in Israel called a knessiah gathering. Agudah unites many rabbinic leaders from the Hasidic wing with those of the non-Hasidic "Yeshiva" world. In Israel it shares a similar agenda with the Sephardic Shas political party. 
The Agudath HaRabonim (Agudas HaRabbonim), also known as the Union of Orthodox Rabbis of the United States and Canada, is a small Haredi-leaning organization that was founded in 1902. It should not be confused with "The Union of Orthodox Jewish Congregations of America" (see above). While at one time influential within Orthodox Judaism, the Agudath HaRabonnim in the last several decades it has progressively moved further to the right; its membership has been dropping and it has been relatively inactive. Some of its members are rabbis from Chabad (Lubavitch) Judaism; some are also members of the RCA (see above). It is currently most famous for its 1997 declaration (citing Israeli Chief Rabbi Yitzhak HaLevi Herzog, Lubavitcher Rebbe Menachem Mendel Schneerson, and Modern Orthodox Rabbi Joseph Soloveitchik) that the Conservative and Reform movements are "not Judaism at all."
The Igud HaRabonim (also: Igud HaRabanim), the Rabbinical Alliance of America, is a small Haredi organization. Founded in 1944, it claims over 650 rabbis; recent estimates indicate that less than 100 of its members worldwide actually work as rabbis.
The Hisachdus HaRabbonim (also: Hisachduth HaRabbonim), "Central Rabbinical Congress (CRC) of the U.S.A. & Canada", was established in 1952. It is an anti-Zionist Haredi organization, consisting mainly of the Satmar Hasidic group, which has about 100,000 adherents (an unknown number of which are rabbis), and other like-minded Haredi groups.
During the past years, the left-wing Modern Orthodox advocacy group Edah, consisting of American Modern Orthodox rabbis. Most of its membership came from synagogues affiliated with the Union of Orthodox Congregations and RCA (above). Their motto was "The courage to be Modern and Orthodox". Edah ceased functioning recently. Edah
The Bais Yaakov movement, begun in 1917, introduced the concept of formal Judaic schooling for Haredi Orthodox women.