Interstate 691 (abbreviated I-691) is a portion of the Interstate Highway System in Connecticut beginning at Interstate 91 in Meriden and ending at Interstate 84 near the Cheshire-Southington town line. It is 8.92 miles (14.36 km) in length, including 0.54 miles (0.87 km) of the exit ramp to the merge with westbound I-84.

I-691 is also known as the Henry D. Altobello Highway for its entire length.

I-691 is the main east–west highway of the city of Meriden. The freeway actually begins in Middlefield as Route 66, technically becoming I-691 at the junction with I-91 (Exit 11). However, westbound signage indicates I-691 begins at the start of the freeway (just west of Exit 13), while eastbound signage shows I-691 ending at the Route 15 interchange (at eastbound Exit 10 about 0.5 miles (0.80 km) west of the interchange with I-91). To go from I-91 northbound to I-691 westbound (or from I-691 eastbound to I-91 southbound), one must actually use Route 15.

In the 1940s, the I-691 routing was part of a planned US 6A Expressway from Southington to Willimantic. A section of the expressway (from its Middlefield terminus west to Exit 8) first opened in 1966. By 1968, the US 6A designation was dropped in favor of Route 66. The highway was extended west to Exit 4 by 1971. The connection to I-84 was eventually completed in 1987, with the renumbering to I-691 done at the same time. The portion east of I-91 remained as Route 66. Environmental and community groups successfully blocked attempts to extend the freeway east of its present terminus due to potential impacts on a reservoir that provides drinking water for the local area. A compromise was reached in the late 1990s allowing CONNDOT to convert Route 66 from a 2-lane road to a 4-lane divided highway from the eastern end of the I-691 freeway to Route 9 in Middletown. Construction on the Route 66 widening project was completed in 2005.