The process of eliminating, or at least minimizing, critical interfaces in the structural assembly process is shown to be very powerful in reducing overall costs. Generic, but specific, examples are used to illustrate the technique. This approach is compared to the more traditional technique of parts-count reduction, and shown to be the more powerful of the two. The procedure for implementing interface control is known as dimensional management. The location of interfaces is defined by the dimensions, and tolerances, of the many parts in assemblies and subassemblies and by those of any fixtures used. Maximizing the permissible tolerances at any one stage of assembly is shown to be achieved by reducing both the number of assembly steps and the number of assembly fixtures involved. Part-to-part assembly is justified on the basis of the number of critical interfaces it eliminates. The key to interface control is the use of the structure on of one side of an interface to locate that interface, within tolerance, and to design the other side so that it can drape to fit, with neither shimming nor trimming on assembly.