Yahwism, also known as the Israelite religion, was the ancient Semitic religion of ancient Israel and Judah and the ethnic religion of the Israelites. The Israelite religion was a derivative of the Canaanite religion and a polytheistic religion that had a pantheon with various gods and goddesses. The primary deity of the religion and the head of the pantheon was Yahweh, the national god of the kingdoms of Judah and Israel. The majority of scholars hold that the goddess Asherah was the consort of Yahweh, though some scholars disagree. Following this divine duo were second-tier gods and goddesses, such as Baal, Shamash, Yarikh, Mot, and Astarte, with each having priests and prophets, and numbering royalty among their devotees.

The practices of Yahwism included festivals, ritual sacrifices, vow-making, private rituals, and the religious adjudication of legal disputes. For most of its history, the Temple in Jerusalem was not the sole or central place of worship dedicated to Yahweh, with many locations throughout Israel, Judah, and Samaria. However, it was still significant to the Israelite king, who effectively led the national religion as the worldly viceroy of the national god.

Yahwism underwent several recontextualizations and redevelopments as the notion of divinities aside from or comparable to Yahweh was gradually degraded by new religious currents and ideas. Possibly beginning with the emergence of Israel during the Late Bronze Age, the northern Kingdom of Israel and the southern Kingdom of Judah had a joint religious tradition comprising cultic worship of Yahweh. Later theological changes concerning the evolution of Yahweh's status initially remained largely confined to small groups, only spreading to the population at large during the general political turbulence of the 7th and 6th centuries BCE. By the end of the Babylonian captivity, Yahwism began turning away from polytheism — or, by some accounts, Yahweh-centric monolatry — and transitioned towards monotheism, and Yahweh was proclaimed the creator deity and the sole deity to be worthy of worship. Following the end of the Babylonian captivity and the subsequent establishment of Yehud Medinata in the 4th century BCE, Yahwism coalesced into what is known as Second Temple Judaism, from which the modern ethnic religions of Judaism and Samaritanism, as well as the Abrahamic religions of Christianity and Islam, would later emerge.

The central element of ancient Israel's religion through most of the monarchic period was the worship of a god named Yahweh, and for this reason the religion of Israel is often referred to as Yahwism. Yahweh, however, was not the "original" god of Israel. Rather it was El, the head of the Canaanite pantheon whose name forms the basis of the name "Israel" (Hebrew: יִשְׂרָאֵל), and none of the Hebrew patriarchs, tribes of Israel, Judges, or early monarchs have a Yahwistic theophoric name (i.e., a name incorporating the name of Yahweh). It is unclear how, where, or why Yahweh appeared in the Levant; even his name is a point of confusion. The exact date of his first appearance is also ambiguous: the term Israel first enters historical records in the 13th century BCE with the Egyptian Merneptah Stele, and, while the worship of Yahweh is circumstantially attested to as early as the 12th century BCE, there is no attestation of even the name "Yahweh" in the Levant until some four hundred years later with the Mesha Stele (9th century BCE). Because of this, Christian Frevel argues that Yahweh worship was rooted in the Kingdom of Israel and preserved by the Omride clan. Nevertheless, many scholars believe that the shared worship of Yahweh played a role in the emergence of Israel in the Late Bronze Age (circa 1200 BCE).

The earliest known Israelite place of worship is a 12th-century BCE open-air altar in the hills of Samaria featuring a bronze bull reminiscent of the Canaanite El-bull. Early Israel was a society of rural villages, but in time urban centers grew up and society became more structured and complex. The Hebrew Bible gives the impression that the Jerusalem Temple was always meant to be the central (or even sole) temple of Yahweh, but this was not the case; archaeological remains of other temples have been found at Dan on Israel's northern border; Arad; Beersheba; and Motza in the southern region of Judah. Shiloh, Bethel, Gilgal, Mizpah, Ramah, and Dan were also major sites for festivals, sacrifices, vow-making, private rituals, and the adjudication of legal disputes.

During an era of religious syncretism, it became accepted among the Israelite people to consider the Canaanite god El as the same as Yahweh. El was soon thought to have always been the same deity as Yahweh, as evidenced by Exodus 6:2–3. Additionally, onomastic evidence indicates that some ancient Israelite families in the pre-exilic period seem to have syncretized the other Canaanite deities with Yahweh, a phenomenon which some scholars have described as "an inclusive sort of monolatry". According to Theodore J. Lewis, different Israelite locales held different beliefs about El but viewed him as a "regional god" that was not entwined with the monarchic nation-state. Because of this, small-scale sacred places were built instead of temples.

The worship of Yahweh alone began at the earliest with prophet Elijah in the 9th century BCE, and at the latest with prophet Hosea in the 8th; even then it remained the concern of a small party before gaining ascendancy in the exilic and early post-exilic period. The early supporters of this faction are widely regarded as monolatrists rather than monotheists; believing Yahweh was the only god worthy of Israelite worship, not that Yahweh was the only god in existence—a noticeable departure from the traditional beliefs of the Israelites nonetheless. It was during the national crisis of the Babylonian Exile that the followers of Yahweh went a step further and denied that any deities aside from Yahweh existed at all—marking the transition from monolatrism to monotheism, and, by extension, from Yahwism to Judaism. Some scholars date the start of widespread monotheism to the 8th century BCE, and view it as a response to Neo-Assyrian aggression.

In 539 BCE, Babylon fell to the Persians, ending the Babylonian exile. According to Ezra 2, 42,360 of the exiled Israelites returned to Jerusalem. As descendants of the original exiles, they had never lived in Judah; nevertheless, in the view of the authors of the Biblical literature, they, and not those who had remained in the land, were "Israel". Judah, now called Yehud, was a Persian province, and the returnees, with their Persian connections in Babylon, secured positions of authority. Though they represented the descendants of the old "Yahweh-alone" movement, the religion they came to institute was significantly different from monarchic Yahwism. Differences included new concepts of priesthood; a new focus on written law and thus on scripture; and a concern with preserving purity by prohibiting intermarriage outside the community of this new "Israel". This new faith later evolved into Second Temple Judaism. The competing religion of Samaritanism also emerged from the "Yahweh-alone" movement.