The erhu is a violin (fiddle) with two strings which, together with zhonghu, gaohu, and sihu, belongs to the "huqin" family of instruments. It is believed to have originated during the Tang dynasty (618-907) in a Mongolian tribe known as Xi, where an instrument known as the xiqin was being used. During the Song dynasty (960-1279), the instrument was introduced to China and was called "Ji Qin". Soon, the second generation of the huqin was among the instruments played at the imperial banquets. During the Yuan (1206-1368), Ming (1368-1644) and Qing (1644-1911) Dynasties, the golden age of the local operas, the erhu developed rapidly. The erhu then developed several different schools.

Two famous artists - Hua Yanjun (1893-1950) and Liu Tianhua (1895-1932) - made an exceptional contribution to the improvement of the erhu, and it was indeed due to the latter that the erhu, an instrument mainly as accompaniment in operas, became a solo instrument. After the founding of the People's Republic of China (1949), the erhu has undergone an unprecedented development in terms of production, education, and technique. Its repertoire has grown rapidly and is used in solo acts, ensembles and concerti with symphony orchestra. The erhu has become one of the most popular instruments in China.

The sound body of the erhu is a small drum-like case usually made of ebony or sandalwood and snake skins. It usually has a hexagonal shape with a length of approximately 13 cm. The front opening is covered with python skin, while the back is open. The case provides resonance to amplify the vibrations of the strings. The neck of the erhu is about 81 cm long and is manufactured using the same materials as drums. The top of the stem is bent for decoration. The two strings of the erhu are usually tuned D and A. The two tuning handles (pegs) are located close to the end of the stem. There are no frets (in contrast to the lute) or touching board (in contrast to violin).

The player creates different pitches by touching the strings at various positions along the neck of the instrument. The strings are usually made of silk or nylon. Nowadays, metal strings are commonly used. The bow is 76 cm long and is made of reed, which is curved during cooking, and arched with horse hair in the same way as the bow of a violin. However, in the case of the erhu, the horse hair runs between the two strings. In other words, one cannot remove the bow from the instrument unless one of the two strings is taken off or broken.

The erhu sounds similar to the human voice and can imitate many natural sounds such as birds and horses. It is a very expressive instrument, most well-known for playing melancholic tunes, but also capable of playing upbeat melodies.

The erhu often plays an important role in national orchestras. In smaller orchestras, there are usually 2 to 6 erhu, in larger ones, 10 with 12. The erhu plays the same role as the violin in Western orchestras.