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The present extent of glacier ice on Bylot Island, Arctic Canada, is mapped using high-resolution Landsat 7 ETM+ satellite imagery. The island is 43% ice covered, with 4783 km² of ice. Most ice is centered on the northwest-southeast--trending Byam Martin Mountains, flowing outward as radial valley glaciers and piedmont lobes. The largest glacier is 49 km long and 6.5 km wide. The majority of glaciers terminate on land, but many have margins ending in lakes and two calve into the sea. The late summer snowline, mapped from satellite imagery, is highest along the southern and central parts of the island at about 1050 m, with lower values along the east-northeastern margin of the ice down to about 700 m. These snowline-elevation differences suggest a predominant moisture source from the northeast. Several valley glaciers and piedmont lobes have deformed medial moraines and ice-surface foliation suggesting past surge activity. Ten glaciers are interpreted to be of possible surgetype. The modern extent of glaciers is compared with that of two earlier time intervals. First, we have mapped glacier margins in several areas of Bylot Island from aerial photographs acquired in 1958 and 1961. Secondly, former positions of ice fronts are mapped from moraine systems deposited during the Neoglacial maximum and identified on satellite data. Glaciers have retreated from 0.9 to 1.8 km since the Neoglacial maximum about 120 years ago, with most retreat occurring between 1958/1961 and 2001. Approximately 253 km² or 5% of the 1958/1961 ice-covered area has been lost. Overall, marked glacier retreat has occurred, although a few glaciers, possibly of surge-type, show small readvances. This retreat is consistent with observed climate warming in the Canadian Arctic, especially since the 1960s. [ABSTRACT FROM AUTHOR]