Earthquakes provide information on the regional segmentation and seismotectonics of the poorly known boundary between the Eurasian and the North American plates from the Knipovich Ridge to the Laptev Sea continental margin. To this end, we have sorted earthquake epicenter locations and focal mechanism solutions from global and regional catalogs, assessed location errors and network detectabilities, and compiled a well-constrained Arctic Catalog of events north of 72¿N for the period 1955--1999. The seismological data are integrated with bathymetry and potential field data to locate ridge and transform segments along the Arctic mid-oceanic ridge (MOR), and we suggest that the plate boundary is divided into four regional provinces. The Spitsbergen Transform System comprises a series of short ridge and transform segments. The seismicity is constrained to the plate boundary in the south but is diffuse in the north. Gakkel Ridge has clustered and focused seismicity and relatively elongated ridge segments cut by small-offset transforms. A first-order change in axis trend at 60¿E divides the ridge into two areas of different morphology and geophysical character. The West Gakkel Ridge has an accentuated relief and high-amplitude magnetic anomalies, whereas the East Gakkel Ridge has a smoother relief and lower magnetic amplitudes. At the Laptev Sea continental slope, the seismicity indicates that the change from ultraslow seafloor spreading to active continental rifting occurs over a less than 60 km wide continent--ocean transition (COT) with a 150--200 km long sheared margin segment.