This article argues that a radical reconceptualization of the notion of neighborhood was introduced by architects in the United States during WWII in response to the new political, cultural, and economic conditions of the war. The efforts of architects and planners like Oskar Stonorov and Louis Kahn contributed to reconfiguring the organizational principle of the “neighborhood unit” model envisioned by Clarence Perry during the 1920s, transferring the discourse from the domain of urban sociology and technical planning to the realm of the American profession. This article revolves around the unexplored and intense period of architectural experimentation during WWII, when the neighborhood emerged as a vibrant platform for the efforts of professional circles to question the values of American democracy and introduce new participative practices in neighborhood and community design, fostering new forms of collaboration between citizens, governmental agencies, and speculative builders under the leadership of architects. Neighborhood design appeared as the testing ground to renegotiate the role and social responsibility of American architects and a foundational value of post-war American society, while its new meanings were to be renegotiated in post-war city planning and built communities.