The Eastern Gray Squirrel (Sciurus carolinensis), or the Grey Squirrel, depending on region, is a tree squirrel native to the eastern and midwestern United States and to the southerly portions of the eastern provinces of Canada.

It has also been introduced to Britain, where it has spread across the country and has largely displaced the native Red Squirrel, Sciurus vulgaris. In Ireland, the red squirrel has been displaced in several eastern counties, though it still remains common in the south and west of the country. There are concerns that such displacement might happen in Italy.

The Eastern Gray Squirrel tends to be larger and stronger than the Red Squirrel and has been shown to have a greater ability to store fat for winter. The squirrel can therefore compete more effectively for a larger share of the available food, resulting in relatively lower survival and breeding rates among the Red Squirrel. Parapoxvirus may also be a strongly contributing factor; Red Squirrels are fatally affected by the disease, while the Eastern Gray Squirrel is unaffected but thought to be carriers. The Red Squirrel is also less tolerant of habitat destruction and fragmentation which has lead to its population decline, while more adaptable Eastern Gray Squirrel has taken advantage and expanded.