Periodisation in history has been the attempt to categorise historical time into discrete blocks. Historians broadly periodise Indian history into Hindu, Muslim and British or more appropriately Ancient, Medieval and Modern basically on the history of the Northern India with its geographical thrust on the Ganges valley. Such rigors of periodisation hardly justify within their fold the movement of regional history. The present investigation has been an attempt to carry out research on how best the regional history with reference to Arunachal Pradesh stands justified to such historical narratives. It focuses on a sketchy description of history of the origin of the inhabitant-tribes; history seen through social and political development; Ahom and British colonial interests over the areas; sources-led history; periodisation vs. history of Arunachal Pradesh citing conjectures and justifying their relevant reference and non-reference to such historical blocks. This work is expected to throw new light on periodisation- issue of the history of Arunachal Pradesh and ask readers to benefit.