Tawhid (Arabic: توحيد tawḥīd "doctrine of Oneness [of God ]"; also transliterated Tawheed and Tauheed) is the concept of monotheism in Islam. It holds God (Arabic: Allah) is one (wāḥid) and unique (ahad).

The Qur'an asserts the existence of a single and absolute truth that transcends the world; a unique and indivisible being, who is independent of the entire creation. The indivisibility of God implies the indivisibility of God's sovereignty which, in turn, leads to the concept of a just, moral and coherent universe, as opposed to an existential and moral chaos. Similarly, the Qur'an rejects the duality of God arguing that both good and evil generate from God's creative act and asserting that the evil forces have no power to create anything. Islamic theology rejects the doctrine of the Trinity where "the one God exists in three Persons and one substance, Father, Son, and Holy Spirit" as believed in mainstream Christianity and professed in the Nicene Creed. God in Islam is a universal god, rather than a local, tribal or parochial one—is an absolute, who integrates all affirmative values and brooks no evil.

Tawhid constitutes the foremost article of the Muslim profession. The first part of the Shahada is the declaration of belief in the oneness of God. To attribute divinity to a created entity is the only unpardonable sin mentioned in the Qur'an. Muslims believe that the entirety of the Islamic teaching rests on the principle of Tawhid. There is an uncompromising monotheism at the heart of the Islamic beliefs which distinguishes Islam from some other major religions.

Islamic intellectual history can be understood as a gradual unfolding of the manner in which successive generations of believers have understood the meaning and implications of professing God's Unity. Islamic scholars have different approaches toward understanding it. Islamic theology, jurisprudence, philosophy, Sufism, even to some degree the Islamic understanding of natural sciences, all seek to explain at some level the principle of tawhid.