James Bay (French: Baie James) is a large body of water on the southern end of Hudson Bay in Canada. Both bodies of water extend from the Arctic Ocean. James Bay borders the provinces of Quebec and Ontario; islands within the bay (the largest of which is Akimiski Island) are part of Nunavut. The James Bay watershed is the site of several major hydroelectric projects, and is also a destination for river-based recreation. Several communities are located near or alongside James Bay, including a number of Aboriginal communities such as the Kashechewan First Nation and nine communities affiliated with the Crees of northern Quebec.

As with the rest of Hudson Bay, the waters of James Bay routinely freeze over in winter, being the closest of any seawater to the equator to do this.

The bay first came to the attention of Europeans in 1610, when Henry Hudson entered it during his exploration of the larger bay that bears his name. James Bay itself received its name in honour of Thomas James, an English captain who explored the area more thoroughly in 1630 – 1631.