Interstate 95 (I-95) is a part of the Interstate Highway System that runs north–south from Miami, Florida to Houlton, Maine. The highway enters Maine from the New Hampshire state line in Kittery and runs for 303 miles (488 km) to the Canada–United States border at Houlton. It is the only primary Interstate Highway in Maine. In 2004, the highway's route between Portland and Gardiner was changed so that it encompasses the entire Maine Turnpike (including the former I-495 between Falmouth and Gardiner), a toll road running from Kittery to Augusta. As an Interstate Highway, all of I-95 in Maine is included in the National Highway System.

I-95 enters Maine as a six-lane highway from New Hampshire on the Piscataqua River Bridge, which connects Portsmouth, New Hampshire, with Kittery. At mile 0.38, the highway becomes the Maine Turnpike. The highway runs in a general northeasterly direction, parallel with US Route 1 (US 1), at this point. I-95 bypasses the Biddeford/Saco area, with a spur route, I-195, connecting to Old Orchard Beach. A curious wayside within Kennebunk around mile 28 is the historic 19th century Mitchell-Hatch family cemetery, which predates the interstate by 150 years and sits only a mere three feet from the rightmost lane of the northbound route. The cemetery was too controversial to relocate, and as such was left in its place as the turnpike came to expand to the very edge of the burial ground.

I-295 splits eastward from I-95 at mile 44 in Scarborough toward Portland Downtown, and Maine's Midcoast region. At this point, I-95 turns inland to the north, bypassing Portland Downtown while providing access to Portland International Jetport. I-95 narrows from six lanes to four lanes at mile 49 near the Portland-Falmouth border. At mile 53 in Falmouth, the highway meets unsigned I-495, also called the Falmouth Spur. Until January 2004, I-95 followed the Falmouth Spur and I-295 between Falmouth and Gardiner.

I-95 continues north along its concurrency with the Maine Turnpike (which was I-495 prior to 2004) through Gray to Auburn and Lewiston, bypassing the latter two cities to the south. The highway then runs in an easterly direction to meet the northern terminus of I-295 at Gardiner. From there, I-95 parallels the Kennebec River past Augusta and Waterville. The highway then crosses the river at Fairfield and then turns northeast along the Sebasticook River past Pittsfield to Newport.

I-95 then continues east alongside US 2 from Newport to Bangor, where I-395 connects to the city of Brewer. The highway runs along the northern edge of Bangor's center, then turns northeast, following the Penobscot River past Orono and Old Town. (Prior to the early 1980s, I-95 was a super two highway north of Old Town).

The highway continues north, still running near the river, toward Howland. Near Lincoln, I-95 runs north through uninhabited forest land, crossing the Penobscot River at Medway. The highway goes northeast and east, passing a series of small Aroostook County farming towns before reaching Houlton, where it connects to US 2 and New Brunswick Route 95 at the international border. North of Bangor, traffic levels drop noticeably, with an annual average daily traffic of only about 5,000 in northern Penobscot County and going down to as low as 2,000 to 4,000 in Houlton.

The Maine Turnpike Authority (MTA) was created by the Maine Legislature in 1941 to build and operate a toll highway connecting Kittery and Fort Kent. In 1947, the first section of highway, designated the Maine Turnpike, opened between Kittery and Portland. In 1953, the MTA began construction on an extension to the state capital at Augusta using the former right-of-way of the Portland–Lewiston Interurban railway from Portland through West Falmouth. The original turnpike was the largest construction project in the state's history until the construction of the extension, which opened to the public on December 13, 1955.

The Maine Turnpike was the first highway in the nation that was funded using revenue bonds. It remains self-financed and does not receive funding from the state or federal government. When the first section opened in 1947, it was only the second long-distance superhighway in the US following the October 1940 opening of the Pennsylvania Turnpike. For these reasons, the Maine Turnpike was named a National Historic Civil Engineering Landmark by the American Society of Civil Engineers in 1999.