Corburn’s article argues that local knowledge is essential for improving environmental planning in communities facing severe environmental and health risks. Challenging the traditional divide between expert and lay knowledge, the article shows that residents possess situated, practical and experiential understandings that professional models often overlook. Using Greenpoint/Williamsburg in Brooklyn as a case study, Corburn examines how community organisations documented air pollution, risks from dry-cleaning chemicals, subsistence fishing hazards and asthma among Latino residents. These examples show that local residents did not merely provide emotional testimony or political pressure; they produced technically valuable knowledge that altered scientific assessments and exposed gaps in official data. The article identifies four major contributions of local knowledge: epistemology, by expanding the evidence base and correcting professional blind spots; procedural democracy, by including voices usually excluded from technical decision-making; effectiveness, by generating low-cost and contextually appropriate interventions; and distributive justice, by revealing unequal environmental burdens experienced by poor, immigrant and racialised communities. Corburn’s most important claim is that environmental decision-making should be based on co-production, where scientific expertise and community knowledge are brought together rather than treated as separate or hierarchical. Ultimately, the article concludes that planners seeking environmental justice must recognise communities as knowledgeable actors, not passive publics, because local knowledge improves both the scientific quality and democratic legitimacy of environmental health planning.