Judaism is the religion practiced by the Jewish people, and is based on the revelation of God to them at Mount Sinai in the year 1312 B.C.E. According to Judaism, at Mount Sinai God gave the Jews the Torah, which encompasses both the Written Law and the Oral Law, and includes His commandments to the Jewish people. (The Oral Law was written down many generations later in the form of the Talmud.)

Judaism is the oldest monotheistic religion still practiced today, dating back some 3800 years to the era of Abraham. Judaism's texts and traditions have contributed to other monotheistic religions, including Christianity and Islam. Judaism's values and teachings have also been a major influence on Western civilization's ethics and civil laws.

A core principal in Judaism is that God is intimately involved with and concerned with the actions of mankind. Judaism also dictates that its adherents bring holiness into the world on an everyday basis by engaging in the mundane world according to Jewish law.

The largest movements within Judaism today are Orthodox Judaism, Reform Judaism, and Conservative Judaism.

Orthodox Judaism maintains that the Torah given at Mount Sinai is divine and therefore eternal; its laws remain applicable in modern times as when they were given. Orthodox Jews practice Judaism in the same way that it was practiced throughout its history, maintaining the same philosophical and legal framework, and finding precedent for modern application of Torah Law within the body of Oral Law transmitted from generation to generation. Two major subgroups comprise Orthodox Judaism, the Modern Orthodox and Hareidi Orthodox, which differ primarily in their views on the desirability of engaging with the secular world, and the role of Zionism in Judaism.

Reform Judaism began in Germany in the early 19th century with the goal of redefining (or reforming) Judaism to reflect modern culture and values. The basic objective of Reform Judaism is to eliminate those aspects of Jewish belief or practice considered unenlightened, meaningless, or irrational, while retaining those elements of Judaism that remain meaningful in the modern world. Because this distinction will be made differently by different people, central to Reform Judaism is the individual's autonomy to decide for himself which beliefs, customs and values define his Judaism.

Conservative Judaism began in America in the late 19th century as a middle-of-the-road alternative to both Orthodox and Reform Judaism. Conservative Judaism maintains many of the beliefs, customs and practices of Orthodox Judaism, while modernizing or relaxing many of its laws. In practice, Conservative Jewry span a wide spectrum, with some Conservative Jews practicing a version of Judaism nearly identical to Modern Orthodox and others closely aligned to Reform.