Eastern gray squirrels are originally from the open woodlands of eastern North America. They have also been introduced into parts of Europe, where they have made trouble for the smaller red squirrels by competing for food sources and breeding sites. They have also made appearances in South Africa and Australia. They are rather large rodents that can measure more than 21 inches (53 cm) from head to tail, and weigh over a pound. Unfortunately, they are so common they are sometimes viewed as pests. As their name suggests, they have grayish fur, although many individuals have reddish patches and some appear more brownish than gray. Their tails, which have many white hairs, are bushier than those of most other squirrels.

Gray squirrels feed mostly on the nuts and buds of many woodland trees like acorns, walnuts, and seeds. In summer, when they are most active just after dawn and before dusk, the squirrels also eat insects. In winter, when most animals of their size are hibernating, gray squirrels are still out there in the cold eating the stores of food which they buried throughout the previous summer. The may have food stashed away in several thousand places. For sleeping arrangements they can make dens in hollow trees, but are more likely to make nests, from twigs and leaves in the boughs of trees. They like to communicate with each other through varied vocalizations and body posturing and movements.

There are two breeding seasons each year; one beginning that begins in the middle of winter the other in the middle of summer. Males begin to chase females through the trees a few days before they are receptive to mating. After females accept a partner and mating has occurred, litters of usually 3 but sometimes 2 or 4 are born 6 weeks later.