La Perla, Puerto Rico’s most famous informal settlement, developed since the early 1900s outside the fortifications of San Juan’s colonial Old Town, the country’s main tourist attraction. In the mid-twentieth century, La Perla was a symbol of the poverty and deprivation that development and scientifically informed planning attempted to remove.

Since the 1970s, La Perla has been a subject of various improvement plans by the local authority with varying degrees of inhabitant participation. Thus, La Perla is connected with the great hopes and fears of the twentieth century: the promise of modernization and progress and the ensuing disappointments, the limitations of top-down decision-making and expert planning, the distress of poverty and marginalization, the opportunities of self-organization and informality, and the threat of forced relocation imposed by gentrification cycles.

Based on previously unpublished archival materials, this article presents an architectural and planning history of La Perla. It compares building types, ownership structures, and municipal policies throughout the 100 years of La Perla’s existence. The article challenges the distinction that legitimizes formal housing as the rule and informal abodes as an environment that is fundamentally different from the formal city. In La Perla formal and informal did not constitute polar opposites, but have to be regarded as two aspects of the same urbanization process. In this sense, La Perla is an intrinsic part of San Juan’s architectural heritage.