The Ambubachi Mela of Assam is an annual Hindu mela that is held at Kamakhya Temple in Guwahati, Assam. This yearly mela is celebrated during the monsoon season that falls in the Assamese month Ahaar, which is around the middle of June. It is the celebration of the yearly menstruation course of the Goddess Kamakhya. It is believed that the presiding goddess of the temple, Devi Kamakhya, also known as Mother Shakti, goes through her annual cycle of menstruation in this stretch of time. It is also believed that during the monsoon rains, the creative and nurturing power of the 'menses' of Mother Earth becomes accessible to devotees at this site during the Ambubachi mela. There is no idol of the presiding deity, however, she is worshipped in the form of a yoni-like stone instead over which a natural spring flows.

The Ambubachi mela is also known as Ameti or Tantric fertility festival since it is closely associated with the Tantric Shakti cult that is prevalent in the eastern parts of India. Some Tantric Babas make public appearances only during these four days. They remain in seclusion the rest of the year. 

The temple remains closed for three days during the Ambubachi mela because it is believed that mother earth becomes unclean for three days, very much like the traditional women's menstrual seclusion in Hindu culture. During these three days some restrictions are observed by the devotees. These include activities like not cooking, not performing puja (prayer rituals) or reading holy books, no farming etc. After three days, Devi Kamakhya is bathed and other rituals are performed to ensure that the Devi retrieves her purity. The doors of the temple are then reopened and prasad is distributed to the devotees. On the fourth day of the Ambubachi Mela, the devotees are allowed to enter the temple and worship devi Kamakhya.

The prasad is distributed in two forms – Angodak and Angabastra. Angodak literally means the fluid part of the body (or water from the spring) and Angabastra literally means the cloth covering the body - a piece of the red cloth that is used to cover the stone yoni during the days of menstruation of the Goddess.

Prasad is a material substance that is made up of vegetarian food. It is a form of religious offering in both Hinduism and Sikhism. It is generally consumed by the devotees after the worship is done.

Each year, lakhs of pilgrims, starting from Sadhus to householders, from all over India, come to Guwahati in Assam to observe this festival, the Ambubachi Mela. Foreigners from abroad also come to seek blessings of Mother Kamakhya.