The groundhog (Marmota monax), also known as a woodchuck, is a rodent of the family Sciuridae, belonging to the group of large ground squirrels known as marmots. The groundhog is a lowland creature of North America; it is found through much of the Eastern United States, across Canada and into Alaska. It was first scientifically described by Carl Linnaeus in 1758.

The groundhog is also referred to as a chuck, wood-shock, groundpig, whistlepig, whistler, thickwood badger, Canada marmot, monax, moonack, weenusk, red monk, land beaver, and, among French Canadians in eastern Canada, siffleux. The name "thickwood badger" was given in the Northwest to distinguish the animal from the prairie badger. Monax (Móonack) is an Algonquian name of the woodchuck, which means "digger" (cf. Lenape monachgeu). Young groundhogs may be called chucklings.^: 66

The groundhog, being a lowland animal, is exceptional among marmots. Other marmots, such as the yellow-bellied and hoary marmots, live in rocky and mountainous areas. Groundhogs play an important role maintaining healthy soil in woodlands and plains. The groundhog is considered a crucial habitat engineer. Groundhogs are considered the most solitary of the marmot species. They live in aggregations, and their social organization also varies across populations. Groundhogs do not form stable, long-term pair-bonds, and during mating season male-female interactions are limited to copulation. In Ohio, adult males and females associate with each other throughout the year and often from year to year. Groundhogs are an extremely intelligent animal forming complex social networks, able to understand social behavior, form kinship with their young, understand and communicate threats through whistling, and work cooperatively to solve tasks such as burrowing.