Recent studies on Latin American Spatial Governance and Planning Systems (SGPSs) have highlighted the need to focus on alternative processes and mechanisms of land-use management and transformation that, arising and operating alongside the formal ones, contribute to shaping the nature of SGPSs themselves. This paper taps into this ongoing debate by further unfolding this 'other institutionality' and broadening its scope. It does so through the exploration of three case studies - namely the SGPSs of Argentina, Chile, and Uruguay - here analysed in relation to their institutional and legal frameworks and the instruments that are produced. In relation to each case, the local spatial planning practices in intermediary cities are examined, enabling understanding of the nuances of the 'other institutionality' mentioned and the role that the latter plays in the overall SGPS. The analysis shows an ongoing 'judicialisation' of spatial planning in the form of an increasing number of legal actions undertaken by civil society and the mobilisation of legal expertise in addressing the urban conflicts. This phenomenon seems to be related to the lack of updated spatial planning tools and public participatory processes to accompany official spatial planning practices. Overall, these findings open a pathway for further comparative spatial planning studies broadening the concept of the 'other institutionality' in Latin America and beyond and shedding light on the role and impact of the latter within existing SGPSs.