The Connecticut Department of Transportation (CTDOT) maintains a system of state highways to serve the predominant flow of traffic between towns within Connecticut, and to towns in surrounding states.

As of January 1, 2007, the state highway system contains a total of 3,719 miles (5,985 km) of roads (not including ramps and interchange connections), corresponding to approximately 20% of all roads in the state.

All state highways are state-maintained except for several segments (totaling 4 miles) that are locally maintained.

State highways that are special service roads are assigned SSR numbers and are unsigned; these numbers are above 399 and are used for internal CTDOT purposes.

Routes are signed state highways and are assigned numbers from 1 to 399 (with the exception of I-684 and I-691).

All state, U.S. and Interstate highways are part of the same numbering system.

In 1958, Connecticut received approval for the route numbers of its three primary Interstate highways: I-84, I-91, and I-95.

In 1900, the State Highway Department proposed a statewide system of trunk line routes.

State highways were classified into primary, secondary, and service roads.

The current system of unsigned ("secret") routes, including the special service roads, was also created during this renumbering.