Kuk-Ak is to be classified into Ah-ak, Dang-ak, Hyang-ak, Jeong-ak.
Ah-ak : It's the traditional music which is performed at the Royal Court ceremonies in the ancient Korean State and Chosun Dynasty. It is the ancient Chinese music and originally it is called the music for the Chinese religious ceremonies. It was performed at the religious services, which the Court held for Wongu, Sajik, Taemyo, Seonnong, Seonjam and Kongjamyo, and at the national grand banquets. Ah-ak, which we know today, is the music for religious ceremony of Confucian shrine.
Dang-ak: It is the music from Dang Dynasty and the Song, which was flown in the era of the Shilla kingdom and the ancient Korea State. Dang-ak includes the folk music from the Song. It has been coming into the Korean Peninsula from the late Shilla Kingdom to the ancient Korean State. Dang-ak was named to distinguish from Hyang-ak. Dang-ak can be devided by Nakyangchoon, Boheoja, Sooryongeum, Eokchiso, and Hawoonbong.
Hyang-ak: It includes the genuine ancient music before Dank-ak came in and the music from the western side of China before the Dang Dynasty. However, today's folk music is not included. The most music except Ah-ak and Dang-ak from Palace and the intellectual class are included in Hyang-ak.
Jeong-ak: It is the music that was played in Palace and the intellectual class such as Ah-ak, Dang-ak and Hyang-ak. Jeong-ak includes the music for religious services for the Ancestral Shrine of the Royal family, honoring the Royal Court, and for the Civil and Military authority. Also, it includes the musical pieces from Yeominrak, Nakyangchoon, Boheoja, Cheeta, and the derivative music from each musical pieces.
Minsok-ak(Folk music): It is the exact opposite from Jeong-ak. The general public enjoyed Minsok-ak. Minsok-ak covers Sanjo, Pan-Sori, Jabga, Minyo, Nongak. Jabga includes Shibee Jabga, Wheemori Jabga, Seodo Jabga, Santaryung, Gayageum Byungchang, Seon-sori. Besides, there are songs like folk songs which were handed down among the people. These are holding the great portion of Minsok-ak. Most of these were begun as the farmers and the fishers sang when they did the religious services or did working. It happened spontaneously without any particular composer. Emotions of life from the people are simply reflected in those music.

*Most of Korean folk songs are changing lyrics of same rhythm and have refrains. According to the circulation range and the degree of refinement, folk songs are devided to Local and Chang folk songs. Local folk songs are sung in some limited area and have very simple story and rhythm. There are Weeding song, Rice-planting song, Pallbearer song, and the song for leveling a site for a house. Chang folk songs, very polished and spreaded broadly, are performed by professional singer. Chang folk songs includes a brisk and lively folk tune, Grief song, Prostitute ballad and Kangwon Arirang. Each region has different rhythm.
Kyunggi Folk song: It's sung in the area of Kyunggi and Choongchung. Most of those songs are five tune and three long pitch. Also, they are sung in speedy rhythm of Seh-Ma-Chi or the tune performed during exorcism. Therefore, they are very rhythmical and 음계의 평선법을 지녀 분명하다. Folk song, Prostitute ballad, Arirang, Gin-Arirang, Farewell song, Song for Adolescence, Doragee song, Porcelain song, Ohdolddogi, and Ohbongsahn ballad are all included in Kyunggi Folk song category.
NahmDo Folk song: It is sung by people down in Cheonla area. It uses much of the rhythm from Pahn -So-Ri and Sahn-Jo. Joong-Mori and Joong-Joong-Mori are used much and rarely Gin-Yang-Cho(a brisk and lively folk tune) and Ja-Gin-Mori are used in NahmDo Folk song. Being dramatic and holding the deep voice back are two most distinguished things in NahmDo Folk song. It includes Bird song, Yook-Ja-Bae-Gi, Farmer song, Joy ballad, Ja-Gin Yook-Ja-Bae-Gi, Ballad for a Hen Pheasant and Gin-Do Arirang.
SeoDo Folk song: Songs from Hwanghae and Pyungahn area. There are seldom songs that have instrumental accompaniment. Singing style is very unique. It uses a nasal voice. You vibrate your voice with clatter or suddenly vibrate very softly right after the long loud voice. SeoDo Folk song covers Long Prodigal song, Ja-Gin Prodigal song, Song for a prayer to Buddha, Monggeumpo ballad, Grief song, Ja-Gin Arang, and Bae-Dda-Ra-Gi.
DongBu Folk song: It's the song from Kyungsang, Kangwon, and Hamkyung area along the Taebaek Mountains. There are lots of rapid melody and rhythms in KyungsangDo Folk song. It includes Milyang Arirang, Quejeena-Ching-Ching-Na-Ne, Domino ballad, and Barley threshing song. KangwonDo Folk song such as Han-Oh-Baek-Nyeon or Barley threshing song has well-regulated rhythm. However, there's an exception of regulated rhythm like Jeonseon Arirang or Grief song medley from PyunganDo.
Nongak: This is the type of band music which is played by farmers to add to the amusement at group work or big holidays. It is also called Pungmul, Doore, Pungjang or Gut. Nongak is effective to enhance the working efficiency and collaboration while doing hard work like weeding and rice-planting. These days, Nongak became essential in all kinds of big holidays and rituals such as Dongje, Gulipgut and Dooregut.