Rifting between Newfoundland and Iberia occurred in two distinct phases-the first late Triassic to Early Jurassic, the second Late Jurassic to Early Cretaceous-culminating in the creation of the North Atlantic Ocean. A dynamic modeling method is used to examine the implications of multiple phases of rifting on the development of the Newfoundland-Iberia conjugate margins. A set of models based roughly on the Newfoundland and Iberian Margins suggests that, under most conditions in which two rift phases occur, the site of the original rift will not be favored for extension when stretching resumes, because the upper mantle cools and strengthens in the area of the original rift. The models predict a lack of magmatism on these margins and suggest that extension was significantly greater in the second rifting phase than in the first; these predictions agree with geological observations. The models do not predict the existence of highly thinned continental crust on both conjugate margins, however.