The North East region of India comprises eight states - Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland, Sikkim and Tripura.
Amongst these eight states, Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland and Tripura are called the 'Seven Sisters of India' due to their interdependence on each other. These states have multiple similarities in social, economic and political aspects.
However, geographically, Sikkim is not a contiguous part of the North East region, as it is separated by the Siliguri corridor/Chicken's neck corridor.