Ungava Bay (French: baie d'Ungava, pronounced [bɛ d‿œ̃ɡava]; Inuktitut: ᐅᖓᕙ ᑲᖏᖅᓗᒃ/ungava kangiqluk) is a bay in Nunavut, Canada separating Nunavik (far northern Quebec) from Baffin Island. Although not geographically apparent, it is considered to be a marginal sea of the Arctic Ocean for climatic reasons. The bay is roughly oval-shaped, about 260 km (160 mi) at its widest point and about 320 km (200 mi) in length; it has an area of approximately 50,000 km (19,000 sq mi). It is generally fairly shallow, under 150 m (490 ft), though at its border with the Atlantic Ocean depths of almost 300 m (980 ft) are reached.

Although it is quite close to the open Atlantic (separated only by Hudson Strait), Ungava Bay is part of the Arctic Ocean. Ungava Bay is separated from Hudson Bay by the Ungava Peninsula. Of the many islands in Ungava Bay, Akpatok Island is largest. Bathymetric studies suggest that Ungava Bay may be the remnant of an impact crater (age unknown) approximately 225 km (140 mi) in diameter.

The southwestern corner of Ungava Bay vies with the Bay of Fundy for the highest tidal range in the world. Some sources estimate the spring tide range at the mouth of the Leaf River as being as high as 17 m (56 ft). Attempts have been made to study the potential for producing electricity using tidal power in the bay, but this is made difficult by the harsh climate and the fact that the bay is ice-free for only a small part of the year.

Due to the influence of the Labrador Current, summers are too cold for tree growth and all the land surrounding the bay is treeless tundra. Typically, temperatures in summer at Kuujjuaq about 20 km (12 mi) up the Koksoak River are about 7 °C (45 °F), while winter temperatures are about −20 °C (−4 °F). Precipitation averages around 400–450 mm (16–18 in) per year, most of it falling in the summer.

Ungava Bay is surrounded by numerous Inuit villages, the largest of which is Kuujjuaq, at the mouth of the Koksoak River. Iron ore has been mined in the past, but despite the high grade of the ores the impossibility of cheap transportation meant that mining was discontinued in 1980. Traditional Inuit hunting activities still dominate the region's life, along with adventure tourism.

• Hudson Bay drainage basin

• Across Arctic Ungava (1949). An online documentary from the National Film Board of Canada.