Ik Onkar, also spelled Ek Onkar or Ik Oankaar (Gurmukhi: ੴ or ਇੱਕ ਓਅੰਕਾਰ; Punjabi pronunciation: [ɪkː oːəŋkaːɾᵊ]; alternate spellings like Ik Ong Kar and Ek Ong Kar also exist [³²]; literally, "one God", hence interpreted as "There is only one God or one Creator.") is a phrase in Sikhism that denotes the one supreme reality. It is a central tenet of Sikh religious philosophy.

Ik Onkar are the first words of the Mul Mantar and also the opening words of the Sikh holy scripture Guru Granth Sahib. The first symbol "ik" is actually not a word but the Punjabi symbol for the number 1.

Ik (ਇੱਕ) is interpreted as "one and only one, who cannot be compared or contrasted with any other", the "unmanifest, Lord in power, the holy word, the primal manifestation of the Godhead by which and in which all live, move and have their being and by which all find a way back to Absolute God, the Supreme Reality."

Ik Onkar has a distinct spelling in the Gurmukhi script and the phrase is found in many Sikh religious scriptures and inscribed in places of worship such as gurdwaras. Some Sikh flags are decorated with the Ik Onkar glyph.

Ik Onkar is also the opening phrase of the Mul Mantar, present as opening phrase in the Guru Granth Sahib, and the first composition of Guru Nanak and the final salok is by Guru Angad. Further, the Mul Mantar is also at the beginning of the Japji Sahib, followed by 38 hymns and a final Salok by Guru Angad at the end of this composition.

ੴ ਸਤਿ ਨਾਮੁ ਕਰਤਾ ਪੁਰਖੁ ਨਿਰਭਉ ਨਿਰਵੈਰੁ ਅਕਾਲ ਮੂਰਤਿ ਅਜੂਨੀ ਸੈਭੰ ਗੁਰ ਪ੍ਰਸਾਦਿ ॥ ਜਪੁ।। ਆਦਿ ਸਚੁ ਜੁਗਾਦਿ ਸਚੁ ਹੈ ਭੀ ਸਚੁ।। ਨਾਨਕ ਹੋਸੀ ਭੀ ਸਚੁ।।

(Ik Oankaar Sati nāmu karatā purakhu nirabha'u niravairu akāla mūrati ajūnī saibha gura prasādi. Japu.. Ādi sacu jugādi sacu hai bhī sacu.. Nānaka hōsī bhī sacu...)

This Being is one, truth by name, creator, fearless, without hatred, of timeless form, unborn, self-existent, and known by the Guru's grace.

Ik Onkar is the statement of oneness in Sikhism, that is 'there is one God'.