Using Radarsat Synthetic Aperture Radar (SAR) imagery of northern Alaska and northwestern Canada, we calculated a mean climatology of the annual landfast ice cycle for the period 1996–2004. We also present the monthly minimum, mean, and maximum landfast ice extents throughout the study area. These data reveal where and when the landfast is most stable and which sections of the coast are susceptible to midseason breakout events. Stabilization of landfast ice is strongly related to the advance of the seaward landfast ice edge (SLIE) into waters around 18 m deep. Isobaths near this depth are a good approximation for midseason landfast ice extent. Comparison with work from the 1970s suggests a reduced presence of landfast ice in this region of the Arctic, due to later formation and earlier breakup. This will likely lead to an increase in coastal erosion and may also have profound effects upon subsistence activities, which are intimately linked to the timing of marine mammal migration patterns. Interannually, landfast ice formation correlates with the incursion of pack ice into coastal waters, suggesting that the later mean date of formation in recent years may be related to the increasingly northward location of the perennial sea ice edge. The timing of breakup correlates well with onset of thawing air temperatures. Analysis of regional data shows a multidecadal trend toward earlier thaw onset, which suggests that the observed change in breakup dates may be part of a longer-term trend.