The Persian or Perso-Arabic alphabet (Persian: الفبای فارسی‎) is a writing system based on the Arabic script. Originally used exclusively for the Arabic language, the Arabic alphabet was adapted to the Persian language, adding four letters: پ [p], چ [t͡ʃ] (although there is an alphabet تش (a mixture of ﺕ and ﺵ) for that sound), ژ [ʒ], and گ [ɡ]. Many languages which use the Perso-Arabic script add other letters. Besides the Persian alphabet itself, the Perso-Arabic script has been applied to the Urdu alphabet, Sindhi alphabet, Saraiki alphabet, Kurdish Sorani alphabet, Lurish (Luri), Ottoman Turkish alphabet, Balochi alphabet, Punjabi Shahmukhi script, Tatar, Azeri, and several others.

In order to represent non-Arabic sounds, new letters were created by adding dots, lines, and other shapes to existing letters. For example, the retroflex sounds of Urdu are represented orthographically by adding a small ط above their non-retroflex counterparts: د [d̪] and ڈ [ɖ]. The voiceless retroflex fricative [ʂ] of Pashto is represented in writing by adding a dot above and below the س [s] letter, resulting in ښ. The close central rounded vowel [ʉ] of Kurdish is written by writing two ﻭ [u], resulting in ﻭﻭ.