The production of fermented fish in North Eastern India (NEI) is done on a household level with indigenous production technology. Different techniques for fish fermentation are used by the inhabitants of the Eastern Himalayan countries of Nepal, Bhutan and the states West Bengal (Darjeeling Hills), Sikkim, Assam, Arunachal Pradesh, Meghalaya, Tripura, Mizoram, and Manipur. The traditional fermented fish items include ngari, hentak, tungtap, shidal etc. Fermented fish product plays prominent roles such as addition of nutritional value, health benefit to the society, etc. Fish fermentation is a long-standing custom to preserve the fish without the use of additional chemicals and without compromising on the quality; instead, it increases the nutritional value. The present chapter aims to focus on the important techniques of fish fermentation which are practiced throughout North Eastern India.