Persian music is based on twelve principal modal systems: seven primary systems called Dastgah and five secondary systems called Avaz. Each system is divided into a series of melodic sequences linked to each other in an unresolved continuity. These sequences are called Gusheh and their number varies depending on the Dastgah. Each Dastgah or Avaz constitutes a specific scale having three distinct notes: (a) Shahed witness or root note), regarded as the tonal or modal center of the Dastgah (Key); (b) Eest (rest note), a temporary rest place for the melodies before as they gradually incline; and (c) Moteghayer (the variable note), which produces expressive colors. The entire group of the systems taken together constitutes the repertoire of Classical Persian Music or Radeef a word that means arrangement and order. Most of Radeef has no meter and follows a speech-like rhythm, but it also contains rhythmic pieces that normally have drum accompaniments.

The list of various Dastagh and Avaz is as follows:

The compositions are mostly based on the Radeef. They include a Peesh Daramad, sometimes stately or lively piece, as the introduction of the Dastgah played by an ensemble in unison; the Chahar-Mezrab a virtuoso solo number with driving rhythm; the Tasneef (a lyrical song) and a Reng a dance-like piece usually in 6/8 meter.