A major spring and harvest festival in northeast India, Rongker is celebrated by the Karbis who were earlier known as the Mikir and are indigenous to the state. The Karbis are a major important ethnic group of Assam in Northeast India, especially in the hill areas of Assam. The Karbis are the primary inhabitants of the Karbi Anglong district. They are also found in the North Kachar district, Kamrup, Nagaon, and Sonitpur districts of Assam. The Karbis are found in the states of Meghalaya, Arunachal, Manipur, and Nagaland.

The festival does have a specific time although it is usually observed at the beginning of the Karbi New year, Thang thang on February 5. Different villages may observe it at different times depending on their convenience. Rongker is celebrated as a Thanksgiving to God for peace, prosperity and a good harvest as well as asking for their assistance to protect them from any evil harm that may happen to the village. It is a post-harvest festival where the community comes together and celebrates with much pomp and gaiety.

The Kurusar or the priest performs prayers and offers animal sacrifices to appease the Karbi deities and seek their blessings for the welfare of the village and its protection from evil entities and natural calamities. The community believes that non-observance of the ritual will invite misfortune upon the village and its inhabitants. It is a yearly religious festival of the Karbis which is performed by every village. Every Karbi village has an allotted place for performing Rongker and every year, villagers across the entire district form a committee to overlook the preparation for Rongker puja. The festival lasts for three days with all villagers contributing in cash and kind as well as donations collected from neighbouring villages to meet the expenses of the rituals.

10 earthen altars against all the deities are installed on the eastern side of the site where the festival is to be held. They are constructed in a row heading in the south-north direction and named after the deities. The shape of altars is made in such a manner that the respective Gods can rest there comfortably. Although 12 deities are worshipped, only 10 altars are set up. A gourd with a tapering mouth full of the first-made rice beer is placed on the altars in the name of the respective deities and other than that, nothing else is placed on the altars. However, two small branches of bamboo are erected on the altar of Ningding Sarpo, a few branches of Basil and a few bamboo sticks are erected on the altar of Murti and a branch of Fongrong, a kind of tree used for worshipping is placed on the altar of Arlok.

The festival is divided into four major parts. During Sadi, all the deities are invited. In Karkli, the deities are worshipped in two ways – Kibo-Kaba, offering meals to the deities and Koia-abida, which is the offering of areca-nut and betel leaves to the deities. All the menfolk take part in the festival and gather in the particular site in the morning with all items required to worship. The main task is performed by the Kurusar, the main priest, assisted by some other religious specialists, the village headman, an official of the Karbi Kingdom, the youth leader of the village, and a few elderly villagers well-versed in worshipping the deities. It is not mandatory to take bath before performing the rituals but they must be purified by sprinkling water with the leaves of the sacred basil. All the sacrifices are made in the names of the deities except for the deity Bamun, who is vegetarian. Then the thek-kere, the religious specialists predict the future of the village at the heart and intestine of the sacrificed animals. At the end of the ritual, a feast is organised. Rongphu-Rongling-Kangthin is also called the Ajo-Rongker and is performed on the night of the second day. Here, the evil spirits are driven out from the lower to the upper part of the village through dancing. An altar is made at the end of the village road and a chicken is sacrificed in the name of Ajo-Angtarpi. Langhe Rongker is the concluding part of the festival observed on the third day of the festival. It is performed near a ghat by making an altar and sacrificing a cock in the name of Arnam-teke, the tiger god, to prevent tigers from attacking.

During this festival, some taboos are observed. The taboos include things like prohibiting husking, not allowing females to participate in the festival, no one is allowed to take part in any agricultural activities during the festival and none of the villagers is allowed to leave the village.

Traditional Dance performance like Ritnong chingdi, Nimso kerung, Hacha kekan, Chong kedam take place as well as displays of Indigenous games.

There is another kind of Rongker performed on a greater scale which is celebrated every five years and is called Wofong Rongker. Wofong Rongker is performed for the well-being of all the people of the villages that fall within a larger jurisdiction and each village is represented by the village headman and several male village elders and is celebrated for two days.