The third session of the Construction History series focuses on Facades. Steel frames freed exterior walls from structural duties, allowing architects new freedom to develop facades that could respond to changing functional and aesthetic criteria. Developers’ desire for efficiency and natural daylight led to thinner, lighter walls – “veneers” in the dismissive language of early critics and “curtain walls” in the parlance of more enthusiastic designers. Electric lighting, building materials, and environmental controls all played roles in changing skyscraper skins in both New York and Chicago. However, each city’s proximity to varying sources of stone, glass, and terra cotta – coupled with differing approaches to fire codes and the politics of local labor unions – created subtly different approaches to skyscraper facades.