This paper will examine the collaborative practice relationship between Eero Saarinen & Associates and Ammann & Whitney Engineers during their decade-long partnership in designing and documenting three concrete shell projects: Kresge Auditorium, TWA Terminal, and Dulles Airport Terminal. The variable range of the buildings’ formal expressions can be traced back to a corresponding level of involvement and influence from the structural engineers, resulting in a shift of Saarinen’s designs.