The last decade has seen a major Canadian contribution to the understanding of the oceanic crust in the area of the Mid-Atlantic Ridge crest. Intensive investigations using a wide range of geological and geophysical techniques, including drilling from D.V. GLOMAR CHALLENGER, have led to detailed information being available for the ridge crest areas at 37°N and 45°N latitude. The information includes bathymetry, crustal age from magnetic and other methods, crustal lithology and layering, basalt petrology, geochemistry and alteration, heat flow, and the physical properties of crustal rocks. From this information significant new models of crustal formation, tectonics, and evolution have been developed. Important features of these models are the episodicity of crustal formation processes on time scales of the order of 105 years or less, the need to search for magnetic anomaly sources at depth in the oceanic crust, and the suggestion that the upper part of basaltic oceanic layer 2 is highly disturbed tectonically. Contributions to knowledge of North Atlantic ocean islands, representing areally small but typical parts of oceanic crust, have come from a series of drilling investigations. Major results include the two-stage formational history of the Bermuda seamount and evidence for large and rapid subsidence, and for active geothermal systems in Iceland and the Azores.