Tawhid (Arabic: توحيد‎ tawḥīd, meaning “unification or oneness of God”; also romanized as Tawheed, Touheed, Tauheed or Tevhid[2]) is the indivisible oneness concept of monotheism in Islam.[3] Tawhid is the religion's central and single most important concept, upon which a Muslim's entire religious adherance rests. It unequivocally holds that God is One (Al-ʾAḥad) and Single (Al-Wāḥid).[4][5]

Tawhid constitutes the foremost article of the Muslim profession of submission.[6] The first part of the shahada (the Islamic declaration of faith) is the declaration of belief in the oneness of God.[4] To attribute divinity to anything or anyone else, is shirk – an unpardonable sin according to the Qur'an, if repentance is not sought afterwards.[7][8] Muslims believe that the entirety of the Islamic teaching rests on the principle of Tawhid.[9]

From an Islamic standpoint, there is an uncompromising monotheism at the heart of the Islamic beliefs (aqidah) which is seen as distinguishing Islam from other major religions.[10] Moreover, Tawhid requires Muslims not only to avoid worshiping multiple gods, but also to relinquish striving for money, social status or egoism.[11]

The Qur'an asserts the existence of a single and absolute truth that transcends the world; a unique, independent and indivisible being, who is independent of the entire creation.[12] God, according to Islam, is a universal God, rather than a local, tribal, or parochial one—God is an absolute, who integrates all affirmative values and brooks no evil.[7]

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.[13]

The classical definition of tawhid was limited to declaring or preferring belief in one God and the unity of God.[14] Although the monotheistic definition has persisted into modern Arabic, it is now more generally used to connote “unification, union, combination, fusion; standardization, regularization; consolidation, amalgamation, merger”.[15]

Chapter 112 of the Quran, titled Al-'Ikhlās (The Sincerity) reads:

Say: “He is Allah, [who is] One. Allah, the Eternal Refuge. He neither begets nor is born, Nor is there to Him any equivalent.”[16]