In Judaism, God has been conceived in a variety of ways. Traditionally, Judaism holds that YHWH, the God of Abraham, Isaac, and Jacob and the national god of the Israelites, delivered the Israelites from slavery in Egypt, and gave them the Law of Moses at biblical Mount Sinai as described in the Torah. According to the rationalist stream of Judaism articulated by Maimonides, which later came to dominate much of official traditional Jewish thought, God is understood as the absolute one, indivisible, and incomparable being who is the ultimate cause of all existence. Traditional interpretations of Judaism generally emphasize that God is personal yet also transcendent, while some modern interpretations of Judaism emphasize that God is a force or ideal.
The name of God used most often in the Hebrew Bible is the Tetragrammaton (YHWH Hebrew: יהוה). Jews traditionally do not pronounce it, and instead refer to God as HaShem, literally "the Name". In prayer the Tetragrammaton is substituted with the pronunciation Adonai, meaning "My Master".
The national god of the Iron Age kingdoms of Israel (Samaria) and Judah was Yahweh. The precise origins of this god are disputed, although they reach back to the early Iron Age and even the Late Bronze.  His name may have begun as an epithet of El, head of the Bronze Age Canaanite pantheon, but earlier mentions are in Egyptian texts that place him among the nomads of the southern Transjordan.
After evolving from its monolatristic roots, Judaism became strictly monotheistic. No consensus has been reached by academics on the origins of monotheism in ancient Israel, but Yahweh "clearly came out of the world of the gods of the Ancient Near East."
The worship of multiple gods (polytheism) and the concept of God having multiple persons (as in the doctrine of Trinity) are equally unimaginable in Judaism. The idea of God as a duality or trinity is heretical in Judaism – it is considered akin to polytheism.
God, the Cause of all, is one. This does not mean one as in one of series, nor one like a species (which encompasses many individuals), nor one as in an object that is made up of many elements, nor as a single simple object that is infinitely divisible. Rather, God is a unity unlike any other possible unity. (Maimonides, 13 Principles of Faith, Second Principle)
Since, according to the mystical conception, all of existence emanates from God, whose ultimate existence is not dependent on anything else, some Jewish sages perceived God as interpenetrating the universe, which itself has been thought to be a manifestation of God's existence. According to this line of theological speculation, Judaism can be regarded as being compatible with panentheism, while always affirming genuine monotheism.
Kabbalistic tradition holds that the divine consists of ten sefirot (attributes or emanations). This has been described as a strand of Judaism which may seem at odds with Jewish commitments to strict monotheism, but Kabbalists have consistently emphasized that their traditions are strictly monotheistic.
Any belief that an intermediary between humanity and God could be used, whether necessary or even optional, has traditionally been considered heretical. Maimonides writes that
God is the only one we may serve and praise....We may not act in this way toward anything beneath God, whether it be an angel, a star, or one of the elements.....There are no intermediaries between us and God. All our prayers should be directed towards God; nothing else should even be considered.
Some rabbinic authorities disagreed with this view. Notably, Nachmanides was of the opinion that it is permitted to ask the angels to beseech God on our behalf. This argument manifests notably in the Selichot prayer called "Machnisay Rachamim", a request to the angels to intercede with God.
In the philosophy of Maimonides and other Jewish-rationalistic philosophers, there is little which can be known about the Godhead, other than its existence, and even this can only be asserted equivocally.
How then can a relation be represented between God and what is other than God when there is no notion comprising in any respect both of the two, inasmuch as existence is, in our opinion, affirmed of God, may God be exalted, and of what is other than God merely by way of absolute equivocation. There is, in truth, no relation in any respect between God and any of God's creatures.— Maimonides, Moreh Nevuchim (Pines 1963)
In Kabbalistic thought, the term "Godhead" usually refers to the concept of Ein Sof (אין סוף), which is the aspect of God that lies beyond the emanations (sephirot). The "knowability" of the Godhead in Kabbalistic thought is no better that what is conceived by rationalist thinkers. As Jacobs (1973) puts it, "Of God as God is in Godself—Ein Sof—nothing can be said at all, and no thought can reach there".
Ein Sof is a place to which forgetting and oblivion pertain. Why? Because concerning all the sefirot, one can search out their reality from the depth of supernal wisdom. From there it is possible to understand one thing from another. However, concerning Ein Sof, there is no aspect anywhere to search or probe; nothing can be known of it, for it is hidden and concealed in the mystery of absolute nothingness.— David ben Judah Hehasid, Matt (1990)
In modern articulations of traditional Judaism, God has been speculated to be the eternal, omnipotent and omniscient creator of the universe, and the source of morality. God has the power to intervene in the world. Maimonides describes God in this fashion: "The foundation of all foundations and the pillar of wisdom is to know that there is a Primary Being who brought into being all existence. All the beings of the heavens, the earth, and what is between them came into existence only from the truth of His being."
Jews often describe God as omniscient, although some prominent medieval Jewish philosophers held that God does not have complete foreknowledge of human acts. Gersonides, for example, argued that God knows the choices open to each individual, but that God does not know the choices that an individual will make. Abraham ibn Daud believed that God was not omniscient or omnipotent with respect to human action.
Jews often describe God as omnipotent, and see that idea as rooted in the Bible. Some modern Jewish theologians have argued that God is not omnipotent, however, and have found many biblical and classical sources to support this view.
Although God is referred to in the Tanakh with masculine imagery and grammatical forms, traditional Jewish philosophy does not attribute gender to God. Although Jewish aggadic literature and Jewish mysticism do on occasion refer to God using gendered language, for poetic or other reasons, this language was never understood by Jews to imply that God is gender-specific.
Kabbalistic tradition holds that emanations from the divine consist of ten aspects, called sefirot.
Most of classical Judaism views God as a personal god, meaning that humans can have a relationship with God and vice versa. Rabbi Samuel S. Cohon wrote that "God as conceived by Judaism is not only the First Cause, the Creative Power, and the World Reason, but also the living and loving Father of Men. He is not only cosmic but also personal....Jewish monotheism thinks of God in terms of definite character or personality, while pantheism is content with a view of God as impersonal." This is shown in the Jewish liturgy, such as in the Adon Olam hymn, which includes a "confident affirmation" that "He is my God, my living God...Who hears and answers." Edward Kessler writes that Hebrew Bible "portrays an encounter with a God who cares passionately and who addresses humanity in the quiet moments of its existence." British chief rabbi Jonathan Sacks suggests that God "is not distant in time or detached, but passionately engaged and present".
The "predicate 'personal' as applied to God" does not necessarily mean that God is corporeal or anthropomorphic, views that Jewish sages sometimes rejected; rather, "personality" refers not to physicality, but to "inner essence, psychical, rational, and moral". However, other traditional Jewish texts, for example, the Shi'ur Qomah of the Heichalot literature, describe the measurements of limbs and body parts of God.
Jews believe that "God can be experienced" but also that "God cannot be understood," because "God is utterly unlike humankind" (as shown in God's response to Moses when Moses asked for God's name: "I Am that I Am"). Anthropomorphic statements about God "are understood as linguistic metaphors, otherwise it would be impossible to talk about God at all".
According to some speculations in traditional Judaism, people's actions do not have the ability to affect God positively or negatively. The Book of Job in the Hebrew Bible states: "Gaze at the heavens and see, and view the skies, which are higher than you. If you sinned, how do you harm God, and if your transgressions are many, what do you do to God? If you are righteous, what do you give God? Or what does God take from your hand? Your wickedness [affects] a person like yourself, and your righteousness a child of humanity." However, a corpus of traditional Kabbalistic texts describe theurgic practices that manipulate the supernal realms, and Practical Kabbalah (Hebrew: קבלה מעשית) texts instruct adepts in the use of white magic.
A notion that God is in need of human beings has been propounded by Abraham Joshua Heschel. Because God is in search of people, God is accessible and available through time and place to whoever seeks Him, leading to a spiritual intensity for the individual as well. This accessibility leads to a God who is present, involved, near, intimate, and concerned for and vulnerable to what happens in this world.
Although the dominant strain in Judaism is that God is personal, modern Jewish thinkers claim that there is an "alternate stream of tradition exemplified by ... Maimonides", who, along with several other Jewish philosophers, rejected the idea of a personal God.
Modern Jewish thinkers who have rejected the idea of a personal God have sometimes affirmed that God is nature, the ethical ideal, or a force or process in the world.
Baruch Spinoza offers a pantheist view of God. In his thought, God is everything and everything is God. Thus, there can be conceived no substance but God. In this model, one can speak of God and nature interchangeably. Although Spinoza was excommunicated from the Jewish community of Amsterdam, Spinoza's concept of God was revived by later Jews, especially Israeli secular Zionists.
Hermann Cohen rejected Spinoza's idea that God can be found in nature, but agreed that God was not a personal being. Rather, he saw God as an ideal, an archetype of morality. Not only can God not be identified with nature, but God is also incomparable to anything in the world. This is because God is “One,” unique and unlike anything else. One loves and worships God through living ethically and obeying His moral law: “love of God is love of morality.”
Similarly, for Emmanuel Levinas, God is ethics, so one is brought closer to God when justice is rendered to the Other. This means that one experiences the presence of God through one’s relation to other people. To know God is to know what must be done, so it does not make sense to speak of God as what God is, but rather what God commands.
For Mordecai Kaplan, the founder of Reconstructionist Judaism, God is not a person, but rather a force within the universe that is experienced; in fact, anytime something worthwhile is experienced, that is God. God is the sum of all natural processes that allow people to be self-fulfilling, the power that makes for salvation. Thus, Kaplan’s God is abstract, not carnate, and intangible. It is important to note that, in this model, God exists within this universe; for Kaplan, there is nothing supernatural or otherworldly. One loves this God by seeking out truth and goodness. Kaplan does not view God as a person but acknowledges that using personal God-language can help people feel connected to their heritage and can act as “an affirmation that life has value.”
Likewise, Rabbi Zalman Schachter-Shalomi, the founder of the Jewish Renewal movement, views God as a process. To aid in this transition in language, he uses the term “godding,” which encapsulates God as a process, as the process that the universe is doing, has been doing, and will continue to do. This term means that God is emerging, growing, adapting, and evolving with creation. Despite this, conventional God-language is still useful in nurturing spiritual experiences and can be a tool to relate to the infinite, although it should not be confused with the real thing.
According to the Pew Forum on Religion and Public Life's 2008 U.S. Religious Landscape Survey, Americans who identify as Jewish by religion are twice as likely to favor ideas of God as "an impersonal force" over the idea that "God is a person with whom people can have a relationship".