This lecture continues the study of the Chicago School, focusing on how architects addressed the aesthetic problem of the tall office building after solving its structural and technological challenges. It examines the transition from early steel-frame skyscrapers to a coherent architectural expression suited to height. Through key works by William Le Baron Jenney and Louis Sullivan, the lecture explains ideas such as tripartite division, grid-based façades, large windows, curtain walls, and minimal ornamentation, culminating in the principle of “form follows function.” Case studies including the Home Insurance Building, Wainwright Building, Guaranty Building, and Carson Pirie Scott Department Store demonstrate how the Chicago School laid the foundations of modern high-rise architecture and influenced skyscraper design across the world.