This dissertation aims to investigate the ideas and work of Louis Kahn and Robert Venturi, who have been considered key figures in what has been called the Philadelphia School, and as exceptionally influential architects in the postwar period. The investigation reveals that although they had different ideas regarding the design of modern architecture, they targeted the same goal—evading the dead end of orthodoxy modernism. More importantly, it appears that they shared several ideas, especially those related to the facade design. In particular, they perceived the facade as an interface between the building and its surroundings, not just a face of the building. Their facades, thus, can be seen to be multi-layered, which is to say composed of two, or more, layers. The outer layer deals with the exterior conditions while the inner layer serves the interior functions. Moreover, they also utilized the facade as a means for dealing with spatial issues. In view of these findings, I describe their facades as “spatially layered.” The development of Kahn’s ideas of the facade unfolded in two stages. In the mid 1950s, Kahn used the facade to organize spatial hierarchies and convey the sense of monumentality. I define this type of facade as the “hollow facade.” When his interest shifted from spatial organization to the utilization of natural light in the late 1950s, he introduced a new version of the facade, which I define it as the “wrapping facade.” While Kahn never explicitly discussed his ideas of the facade, Venturi demonstrated his interest in the facade throughout his writings. Venturi’s ideas of the facade can be categorized into two types. In his seminal book, Complexity and Contradiction in Architecture, he introduced a kind of facade that aims at creating visual and spatial complexity and contradiction, which I call the “layered facade.” When he shifted his focus to the issue of iconography in architecture, he developed the “decorated facade.” These facades manifest types of the spatially layered facade and differentiate their buildings from others nearby. In addition, it is found that these facades feature some shared attributes—including adaptable space, functional monumentality, hidden main entrances, T-shaped windows, and oversized elements, which significantly characterize Philadelphia School architecture.