The Great Lakes St. Lawrence Seaway Development Corporation (GLS) is a wholly owned government corporation which operates and maintains that part of the St. Lawrence Seaway within the territorial limits of the United States and which encourages the development of trade through the Great Lakes/St. Lawrence Seaway System, a waterborne, direct route to and from the heartland of North America.

The Great Lakes and the St. Lawrence River combine to form the longest deep-draft navigation system in the world, extending 3,700 kilometers (2,300 miles) into the North American heartland. The system includes the five Great Lakes and their connecting channels, as well as the St. Lawrence River to the Gulf of St. Lawrence. A series of locks either lift or lower vessels to overcome elevation changes. GLS serves the U.S. intermodal and international transportation system by improving the operation and maintenance of this safe, reliable, efficient, and environmentally responsible deep-draft waterway.