The U.S. Army Corps of Engineers planned and supervised the construction of the United States' section of the St. Lawrence Seaway. The project was both a massive engineering effort and an unusually complicated exercise in intergovernmental cooperation. Local, state, and federal agencies shared a concern with finishing the project as quickly and competently as possible. However, inevitably disagreements occurred over timetables, budgets, and priorities. There was also the general concern with meeting our commitment to Canada, which had assumed the responsibility for constructing most of the Seaway. This history is an analysis of the planning and engineering effort of the Corps of Engineers on the Seaway project. More than that, the author addresses the various political issues that often influenced the engineers. Because of the scale of operations, the large number of governmental bodies involved, and the even greater number of contractors and subcontractors, the story of the construction of the St. Lawrence Seaway offers significant insights into problems facing federal engineers in developing huge international projects. Paul W. Taylor Colonel, Corps of Engineers Chief of Staff