The design and construction of skyscrapers involves creating safe, habitable spaces in very tall buildings. The buildings must support their weight, resist wind and earthquakes, and protect occupants from fire. Yet they must also be conveniently accessible, even on the upper floors, and provide utilities and a comfortable climate for the occupants. The problems posed in skyscraper design are considered among the most complex encountered given the balances required between economics, engineering, and construction management. One common feature of skyscrapers is having a steel framework from which curtain walls are suspended, rather than load-bearing walls of conventional construction. Most skyscrapers have a steel frame that enables to build taller than load-bearing walls of reinforced concrete. Skyscrapers usually have particularly small surface area of what are conventionally thought of as walls, because the walls are not load-bearing and therefore most skyscrapers are characterized by large surface areas of windows made possible by the concept of steel frame and curtain walls. One Worldwide Plaza is part of a three building, mixed use commercial and residential complex completed in 1989, in the borough of , known collectively as Worldwide Plaza. One Worldwide Plaza is a commercial office tower on Eighth Avenue. Two Worldwide Plaza is a residential condominium tower west of the center of the block, and Three Worldwide Plaza is a low rise condominium residential building with street level stores on , to the west of the towers. Skidmore, Owings & Merrill was the designer for the office complex and the residential complex was designed by Frank Williams.

The Flatiron Building, originally the Fuller Building, is located at 175 Fifth Avenue in the borough of Manhattan, New York City, and is considered to be a groundbreaking skyscraper. Upon completion in 1902, it was one of the tallest buildings in the city and one of only two skyscrapers north of 14th Street the other being the Metropolitan Life Insurance Company Tower, one block east. The building sits on a triangular island block formed by Fifth Avenue, and East 22nd Street, with 23rd Street grazing the triangle's northern (uptown) peak. As with numerous other wedge shaped buildings, the name Flatiron derives from its resemblance to a cast- iron clothes iron. Willis Tower (formerly named and still commonly referred to as Sears Tower) 1,451foot skyscraper in , Illinois. At the time of its completion in 1973, it was the tallest building in the world, surpassing the World Trade Center towers in New York, and it held this rank for nearly 25 years. Willis Tower is the second tallest building in the United States and the eighth tallest freestanding structure in the world. The skyscraper is one of the most popular tourist destinations in Chicago, and over one million people visit its observation deck each year. Named the Sears Tower throughout its history, in 2009 the Willis Group obtained the right to rename the building, as part of their lease on a portion of its offices. On July 16, 2009, the building was officially renamed Willis Tower.