The Chicago School was a decisive moment in the emergence of the modern skyscraper. The lecture explains how rapid urbanization, industrial growth, land pressure, and new technologies in late 19th-century Chicago led to the development of the tall office building. It examines key factors such as steel-frame construction, passenger elevators, fireproofing systems, grid-iron city planning, and the shift from load-bearing masonry to curtain wall construction. Through early examples like the Haughwout Building and the Monadnock Building, the lecture highlights how functional needs, structural innovation, and economic efficiency shaped a new architectural language that laid the foundations for modern high-rise architecture.