The birth of a warm core ring is conceptualized as a catastrophic separation process governed by the strong inertial forces within a western boundary current. A frictionless theory based on this postulate and assumed geostrophic balance on completion of the separation process yields a description of ring geometry and velocity distribution in first-order agreement with observation. In particular, maximum velocities of the order of 1 m s-1 are predicted to occur near the perimeter. The initial decay rate of the ring is estimated from an interface friction and entrainment model (using the above maximum velocity) to be about 0.05 day-1, which reduces rapidly, however, as the ring slows down. Interface friction is found to be much more important than entrainment in producing the decay.