The Northern Bog Lemming, Synaptomys borealis is a small North American lemming. This is one of two species in genus Synaptomys, the other being the Southern Bog Lemming.

They have cylindrical bodies covered with long grey or brown fur with pale grey underparts. There is a patch of rust-coloured hair at the base of the ears. They have small eyes, a hairy snout and a short tail. They have 16 teeth and their upper incisors are grooved. They are 13 cm long with a 2 cm tail and weigh about 30 g.

These animals are found in wet northern forests, bogs, tundra and meadows in Canada, Alaska and northern Washington and New England. They feed on grasses, sedges, other green vegetation and mosses, also snails and slugs. Their droppings are green. Predators include owls, hawks, mustelids and snakes.

Female lemmings have 2 or 3 litters of 4 to 6 young in a year. The young are born in a nest in an underground burrow or concealed in vegetation.

They are active year round, day and night. They make runways through the surface vegetation and also dig underground burrows. They burrow under the snow in winter. These animals are often found in small colonies. Lemming populations go through a 3 or 4 year cycle of boom and bust.