The Thomas P. "Tip" O'Neill Jr. Tunnel is a highway tunnel built as part of the Big Dig in Boston, Massachusetts. It carries the Central Artery underneath downtown Boston, and is numbered as Interstate 93 (I-93), U.S. Route 1 (US 1), and Route 3. It roughly follows the route of the old elevated Central Artery, though the northbound entrance, at the corner of Kneeland Street and Atlantic Avenue, is somewhat east of the southbound exit to allow for a reconfigured interchange with the Massachusetts Turnpike. It runs from the Zakim Bunker Hill Bridge at its north portal—barely 165 feet (50 m) east of the TD Garden sports facility's eastern corner—to Boston's Chinatown at its south portal. The tunnel is named for Tip O'Neill, former Speaker of the United States House of Representatives, whose constituency included several of the surrounding communities in Metro Boston.

The Big Dig was a megaproject in Boston that rerouted the then elevated Central Artery of Interstate 93 that cut across Boston into the O'Neill Tunnel and built the Ted Williams Tunnel to extend Interstate 90 to Logan International Airport. Those two projects were the origin of the official name, the Central Artery/Tunnel Project. Additionally, the project constructed the Zakim Bunker Hill Bridge over the Charles River, created the Rose Kennedy Greenway in the space vacated by the previous I-93 elevated roadway, and funded more than a dozen projects to improve the region's public transportation system. Planning for the project began in 1982; the construction work was carried out between 1991 and 2006; and the project concluded on December 31, 2007. The project's general contractor was Bechtel and Parsons Brinckerhoff was the engineer, who worked as a consortium, both overseen by the Massachusetts Highway Department.