Iran's musical instruments have been of immense importance since ancient times.
Around a hundred years ago, Iran's music was gradually separated from songs and followed its own way Iranian musicians and composers mastered the Iranian musk and made innovations in this regard but, on the whole, Iran's Instrumental music, has two main parts:

1) solo which is based on traditional music and improvisation.

2) Group playing, either small or large groups with solo or chorus.

Solo
Solo is highly significant in oriental music and this can be related to the eastern philosophy and mysticism and making a connection with the spiritual world.

Group Playing
Group playing became more common in Iran since the time of Nasereddin Shah the Qajar king. It was both in the form of traditional music and
Instruments and martial music and western instruments which were introduced in Iran by Monsieur Loumer (the French music teacher who had been invited to Iran to teach at Darolphonoon school) later, group playing became more common and with western musical instruments joining the Iranian ones and the playing of Iranian pieces on western Instruments, It further prospered.
The oldest Iranian musical instruments are the ney (the Iranian flute) and the tambourine. The following are the different kinds of Iranian musical instruments generally classified: 

Wind Instruments
The ney is the oldest instrument in this group. It is a tube made of cane with seven joints and six knots. The ney is among Iran's rural instrument and it usually played in all parts of lran.

Another Iranian wind instrument is Sorna (an oboe-like Iranian instrument) which is common all over lran and is of two types: Bakhtyari and Azarbaijani. In Iran, the Sorna is usually accompanied by the Dohol or the naghareh (a drum-like Iranian Instrument). This instrument is played at different occasions according to the particular region of the country. In the Kurdistan region of Iran, the dohol and the sorna are played at mourning ceremonies while in the north, the soma is played along with the performance of ropewalkers and West Azarbaijani, the villagers play the Sorna in their marriage ceremonies along with wood dancing.

The Korna is an ancient and historical instrument, which is made and played differently In various provinces Iran. The main types of the Korna (an Iranian instrument of the sorna family) are those in the north ciran, Gilan and Mashhad. The Korna is mostly played in Kordestan and Azarbaijan.
The Bagpipe: It is mostly used in the south of iran. In some parts of Iran, it is called "Khiknai". It is also played in some parts of Azarbaijan. 

String Instruments
The unique Iranian musical instrument in this group is the Santour. It consists of a trapezoid wooden box over which 72 white (high) and yellow (bass) strings have been stretched. It has two wooden sticks. The santour is an instrument which can be played both solo and in group and it is played in all parts of lran.

One of the oldest string Instruments is Kamancheh (an Iranian violin-like instrument resting on the ground during the performance). This instrument can be used well both in solo and in-group performance. Kamancheh is a national musical instrument, which is played in all the provinces of Iran, but is mostly common among Turkmen and Turk tribes.

The barbat (a harp-like Iranian instrument) is an instrument from the family of limited string instruments. It is also called Oud or Lout. Its body is like a pear divided lengthwise into two parts. It has a big body and a short neck which, in earlier times, used to have three strings. The rabab or robab has four parts: a melon-shaped body, middle, neck, and head. The strings of the rabab used to be made of the she-bowel, but now they are made of nylon threads. Its plectrum is made of chicken feather. This instrument is mainly rural and is mostly played in Khorasan and also in some parts of Baluchistan and Sistan.

The tar is one of the original Iranian string instruments, It has a multi-part body and six strings. Other musical instruments of the tar family are the Dotar and the Setar. The dotar is usually played in Turkmen Sahra and Khorasan.