This paper explores the development of peripheral neighborhoods in Santiago, Chile, during the 1950s and 1960s, challenging the notion that they emerged spontaneously or informally. Instead, it argues that these urban areas were the result of planned yet diverse projects involving state institutions, technical professionals, and local communities. While influenced by global models, these initiatives were primarily shaped by Chile's specific socio-political and economic contexts. The concept of “peripheral urbanism” is introduced to describe these processes, emphasizing the significant but often overlooked role of architects, urban planners, engineers, and other experts in shaping the urban peripheries. The study examines two key cases: the Aided Self-Help Housing program and Operación Sitio, both of which illustrate how technical expertise, policy decisions, and grassroots mobilization interacted to address the housing problem. Although Santiago’s peripheral neighborhoods did not emerge from conventional planning frameworks, at least not in the North American or European sense, they were not informal developments. Rather, they resulted from a complex array of projects and policies driven by multiple actors. By reevaluating these locally situated processes, this study contributes to a more nuanced understanding of urban development and urbanism in Latin America and beyond.