Smith, J.V., 1993. Infinitesimal kinematics of rotational rifting with reference to en echelon marginal faults in the Red Sea region. Tectonophysics, 222: 227–235. Many rifts open obliquely to the trend of the rift, commonly forming en echelon patterns of extensional structures on the rift margins. Previously, the kinematics of such rifts have been modelled theoretically and experimentally, assuming translational movement of the rifted blocks. The actual movements of continental blocks during rifting are commonly rotational about some pole rather than being translational. If the trend of the rift is offset from the pole of rotation then the opening of the rift will be oblique. The degree of obliquity is related to the ratio between the offset of the pole from the rift trend and the distance from the point on the rift to the rotational pole. Consequently, the angle between the displacement (divergence) direction and the rift will vary for differently trending rift segments and even along straight rift segments. Infinitesimal strain theory is used to relate displacement direction at the time of rifting to en echelon patterns of extensional faults along rifted margins. Measurements of the orientation of en echelon structures from published maps of the Red Sea region fit the predictions of the model. Marginal en echelon structures not only provide a way to check poles of rotation determined by other means, but also to determine the steadiness of a pole as rotational rifts propagate laterally through time.