The Thames River is a short river and tidal estuary in the U.S state of Connecticut. It flows south for 25 km. through eastern Connecticut from the junction of the Yantic River and the Shetucket River into Long Island Sound. Norwich is at its head and New London at its mouth.

The river has provided important harbors for many years, since early colonial time when it was known as the Pequot River for the Pequot Indians who lived in the area. The U.S. Coast Guard Academy, a U.S. Navy submarine base, and the port or harbor for New London are located here.