The fundamental concept in Islam is the oneness of God (tawhid). This monotheism is absolute, not relative or pluralistic in any sense of the word. God is described in Sura al-Ikhlas, (chapter 112) as follows: Say "He is God, the one and only. Allah, the Eternal, Absolute the Self-Sufficient master. He begetteth not, nor is he begotten. And there is none like unto Him." (Yusuf A. Ali).

In Arabic, God is called Allāh. The word is etymologically connected to ʾilah "deity", ultimately from Proto- Semitic *ʾilâh-, and indirectly related to Hebrew Ēl. Allāh is also the word used by Christian and Jewish Arabs, translating ho theos of the New Testament and LXX; it predates Muhammad and in its origin does not specify a "God" different from the one worshipped by Judaism and Christianity, the monotheistic religions to which Muhammad's teaching stood in contrast.

The name "Allah" shows no plural or gender, unlike the word "God" that may take plural sense "Gods" and feminine form "Goddesses". In Islam "Allah" Almighty as the Qur’an says: "(He is) the Creator of the heavens and the earth: He has made for you pairs from among yourselves, and pairs among cattle: by this means does He multiply you: there is nothing whatever like unto Him, and He is the One that hears and sees (all things)" (42:11). The implicit usage of the definite article in Allah linguistically indicates the divine unity. Muslims believe that the God they worship is the same as the Judeo-Christian God, i.e. the God of Abraham. However, Muslims reject the Christian theology concerning the trinity of God (the doctrine of the Trinity which regards Jesus as the eternal Son of God), seeing it as akin to polytheism. Quoting from the Qur'an, sura An-Nisa 171: "O People of the Scripture! Do not exaggerate in your religion nor utter aught concerning Allah save the truth. The Messiah, Jesus son of Mary, was only a messenger of Allah, and His word which He conveyed unto Mary, and a spirit from Him. So believe in Allah and His messengers, and say not "three". Cease! (it is) better for you! Allah is only One God. Far is it removed from His transcendent majesty that he should have a son. His is all that is in the heavens and all that is in the earth. And Allah is sufficient as its defender."

No Muslim visual images or depictions of God exist because such artistic depictions may lead to idolatry and are thus prohibited. A similar position in Christian theology is termed Iconoclasm. Moreover, most Muslims believe that God is incorporeal, rendering any two or three- dimensional depictions impossible. Instead, Muslims describe God by the many divine attributes mentioned in the Qur'an. All but one Surah (chapter) of the Qur'an begins with the phrase "In the name of Allah, the Beneficent, the Merciful". These are consequently the most important divine attributes in the sense that Muslims repeat them most frequently during their ritual prayers (called salah in Arabic, and in India, Pakistan and Turkey called "namaaz" (a Persian word)).