Orthodox Judaism is the most religiously stringent of the three main streams of American Judaism. It is the collective term for the traditionalist branches of contemporary Judaism. Orthodox Jews believe in a strict interpretation of Jewish law, or halacha, which they think is grounded in the Torah (the first five books of the Hebrew Bible), both oral and written, and the revelation made to Moses by God on Mount Sinai. They regard the entire halakhic system as ultimately grounded in immutable revelation, essentially beyond external influence. Orthodox Judaism adheres to monotheism, the belief in one God.

Orthodox Jews are not one group, but rather many sub-groups, and arguments rage between them at times as to how strict interpretation of Jewish law should be. However, they do all adhere to certain core beliefs. Orthodox Jews are vastly more likely than non-Orthodox Jews to enroll their children in private religious day schools, to pray daily, and maintain traditional kosher dietary practices. They are more than twice as likely as non-Orthodox Jews to say that being Jewish is very important to them.

Ultra-Orthodox Judaism, also called Haredi Judaism, encompasses several groups within Orthodox Judaism that strictly observe Jewish religious law and separate themselves from Gentile society as well as from Jews who do not follow the religious law as strictly as they do. Ultra-Orthodox communities are found primarily in Israel, where they form about 13 percent of Israel’s population; North America, particularly in New York City; and western Europe.

In summary, Orthodox Jews believe in a strict interpretation of Jewish law, adhere to certain core beliefs, and are more religiously stringent than non-Orthodox Jews.