Passive margin study has been at the core of scientific ocean drilling because it provide important information on processes in continental extension, breakup, and the eventual formation of new oceanic spreading centers. In this paper, ODP investigations in the evolution and characteristic of volcanic & non-volcanic passive margins have been briefly introduced. Drilling on the Iberia-Newfoundland non-volcanic margin by ODP Legs 103, 149 and 173 have demonstrated clearly that low-angle detachment faults have contributed to the unroofing and formation of continent-ocean transition zone, resulting in the exposure of serpentinized and tectonized mantle peridotite. Results from ODP Leg 104, 152 and 163 on volcanic passive margin of Norway-Greenland conjugate pair suggest that the magmatic processes have played a major role in the thinning of crust and the final breakup. Drilling results so far support an asymmetric simple shear mode for the formation of non-volcanic margins. ODP explorations also reveal characteristics of seismic seaward-dipping reflections. For a better understanding of the processes from continental extension to breakup to the final oceanic spreading, further in-depth studies are required in the IODP phase by drilling, sampling across a full rift system on conjugate margin pairs and other locations such as Okinawa Trough and the South China Sea.