Formerly serving as the corporate headquarters for AT&T and Sony, 550 Madison Avenue was a striking departure from the "glass box" design of many high-rise office buildings at the time of its design and construction. Via the use of an innovative structural steel framing system, a host of challenging architectural and engineering requirements were met for the 36-story project in midtown Manhattan. Architect Philip Johnson has called the building his "capolavoro -- the culmination of my life's work."