Judaism (Hebrew: יַהֲדוּת‎‎ Yahăḏūṯ) is an Abrahamic, monotheistic, and ethnic religion comprising the collective religious, cultural, and legal tradition and civilization of the Jewish people. It has its roots as an organized religion in the Middle East during the Bronze Age. Modern Judaism evolved from Yahwism, the religion of ancient Israel and Judah, by the late 6th century BCE, and is thus considered to be one of the oldest monotheistic religions. Judaism is considered by religious Jews to be the expression of the covenant that God established with the Israelites, their ancestors. It encompasses a wide body of texts, practices, theological positions, and forms of organization.

The Torah, as it is commonly understood by Jews, is part of the larger text known as the Tanakh. The Tanakh is also known to secular scholars of religion as the Hebrew Bible, and to Christians as the "Old Testament". The Torah's supplemental oral tradition is represented by later texts such as the Midrash and the Talmud. The Hebrew word torah can mean "teaching", "law", or "instruction", although "Torah" can also be used as a general term that refers to any Jewish text that expands or elaborates on the original Five Books of Moses. Representing the core of the Jewish spiritual and religious tradition, the Torah is a term and a set of teachings that are explicitly self-positioned as encompassing at least seventy, and potentially infinite, facets and interpretations. Judaism's texts, traditions, and values strongly influenced later Abrahamic religions, including Christianity and Islam. Hebraism, like Hellenism, played a seminal role in the formation of Western civilization through its impact as a core background element of Early Christianity.

Within Judaism, there are a variety of religious movements, most of which emerged from Rabbinic Judaism, which holds that God revealed his laws and commandments to Moses on Mount Sinai in the form of both the Written and Oral Torah. Historically, all or part of this assertion was challenged by various groups such as the Sadducees and Hellenistic Judaism during the Second Temple period; the Karaites during the early and later medieval period; and among segments of the modern non-Orthodox denominations. Some modern branches of Judaism such as Humanistic Judaism may be considered secular or nontheistic. Today, the largest Jewish religious movements are Orthodox Judaism (Haredi Judaism and Modern Orthodox Judaism), Conservative Judaism, and Reform Judaism. Major sources of difference between these groups are their approaches to halakha (Jewish law), the authority of the rabbinic tradition, and the significance of the State of Israel. Orthodox Judaism maintains that the Torah and halakha are divine in origin, eternal and unalterable, and that they should be strictly followed. Conservative and Reform Judaism are more liberal, with Conservative Judaism generally promoting a more traditionalist interpretation of Judaism's requirements than Reform Judaism. A typical Reform position is that halakha should be viewed as a set of general guidelines rather than as a set of restrictions and obligations whose observance is required of all Jews. Historically, special courts enforced halakha; today, these courts still exist but the practice of Judaism is mostly voluntary. Authority on theological and legal matters is not vested in any one person or organization, but in the sacred texts and the rabbis and scholars who interpret them.

Jews are an ethnoreligious group including those born Jewish (or "ethnic Jews"), in addition to converts to Judaism. In 2019, the world Jewish population was estimated at 14.7 million, or roughly 0.19% of the total world population. In 2021, about 45.59% of all Jews resided in Israel and another 42.06% resided in the United States and Canada, with most of the remainder living in Europe, and other minority groups spread throughout Latin America, Asia, Africa, and Australia.