Longfellow Bridge, also known to locals as the "Salt and Pepper Bridge" or the "Salt and Pepper Shaker Bridge", carries Route 3 and the MBTA's Red Line across the Charles River to connect Boston's Beacon Hill neighborhood with the Kendall Square area of Cambridge, Massachusetts. A portion of the elevated Charles/MGH train station also rests upon the southern end of the bridge.

The bridge structure was built on the site of the 1793 West Boston Bridge and was originally known as the Cambridge Bridge, but was renamed for Henry Wadsworth Longfellow.

Willam Jackson served as chief engineer and Edmund M. Wheelwright as architect. Wheelwright was inspired by the 1893 Columbian Exposition and was trying to rival the great bridges of Europe.

The bridge opened on August 3, 1906 and consists of 11 steel arch spans on masonry piers. The bridge has a total length of 1,768 feet (539 m) and supports road, subway, and pedestrian traffic. For some reason, the upstream sidewalks are narrower than the downstream.

For a time during the 1990s and early 2000s, the bridge's towers bore several colorful paint splatters placed there by unknown vandals. These splatters remained on the bridge for several years, but were eventually cleaned off by the state.