The Takbīr or Tekbir (تَكْبِير) is the Arabic term for the phrase Allāhu Akbar (الله أكبر). It is usually translated "God is [the] Greatest," or "God is Great". It is a common Islamic Arabic expression. It is used in various contexts by Muslims: in formal prayer, as an informal expression of faith, in times of distress, to express celebration or victory, and to express resolute determination or defiance (especially in politically charged contexts).

The form Allāhu is the nominative of Allah "God". The form akbar is the elative of the adjective kabīr "great", from the root k-b-r. As used in the takbir it is usually translated as "greatest", but some authors prefer "greater". The term takbīr itself is the stem II verbal noun (tafʿīlun) of the triliteral root k-b-r "great".

This phrase is recited by Muslims in many different situations. For example, when they are very happy, to express approval, to praise a speaker, or as a battle cry, during times of extreme stress. In the Islamic world, instead of applause, often someone will shout "takbir" and the crowd will respond "Allahu Akbar" in response.