Analysis of seismic data, 3-D gravity inversion and 2-D forward modelling provided basement configuration, crust thickness and Moho topography, thereby deciphered modes of rift evolution and location of Continent-Ocean Boundary (COB) along margins. The basement near margin, is traversed by coast perpendicular grabens, and their seaward continuity is delineated up to 125 km. Three different types of continental margin evolution are present along the ECMI - 1) sheared rift on southern segment of the ECMI, 2) hyper-extended rift on central segment and 3) hypo-extended rift on northern segment. Structural architecture of both ECMI and offshore Bengal Basin clearly suggests that COB runs nearly parallel to coastline, but takes an orthogonal turn in offshore Bengal Basin and connects paleo-continental shelf and Rajmahal-Sylhet line in onshore Bengal Basin. Crustal thickness and depth to Moho discontinuity beneath Bangladesh margin are unusual as the former is increased by a process of interaction of Kerguelen plume with existed oceanic lithosphere and latter is subsided largely due to excessive Bengal Fan sediment load. Absence of rifted crustal blocks on Bangladesh margin and continuity of COB into onshore Bengal Basin suggest that present Bangladesh region was in marine conditions at least until beginning of Bengal Fan sedimentation.