Key MessagesHigh costs and non-intuitive design of proprietary GIS software pose barriers to marginalized communities.Free and open source GIS provide unique access opportunities. Open GIS-based community information systems act as an alternative to proprietary GIS.Geospatial technologies are central to spatial decision making and governance, but gaining equitable access to these is still difficult for traditionally marginalized communities. We contend that the dominance of proprietary GIS software has contributed to this digital divide, as these are inherently disempowering to marginalized social groups. Their high purchasing cost and licensing fees pose access barriers to resourcepoor citizens. Design of proprietary software may also not be appropriate for marginalized groups who are neither trained in GIS, nor represent the needs of dominant market base. Therefore, "free and open source software for geospatial" (FOSS4G) and open GIS provide new opportunities in democratizing GIS, as these are open code and free of purchasing and licensing costs. This paper aims to discuss the role of open GIS in advancing the goals of public participation GIS (PPGIS). We first discuss the origins of the FOSS movement, and explore the ways it has shaped the FOSS4G and open GIS movements. Next, we examine how a community information system built with open GIS software is being successfully utilized by an environmental organization in Milwaukee, to contest urban poverty. Our research demonstrates that open source GIS offers unique opportunities in advancing PPGIS research and practice.The Canadian Geographer Le Géographe canadien The Canadian Geographer Le Géographe canadien droit de licence. Cet article examine le rôle du logiciel de SIG ouvert en fonction des objectifs du SIG pour la participation publique (SIGPP). Nous discutons d'abord des origines du mouvement du logiciel libre et ouvert puis nous examinons les faS cons dont il a faS conn e le FOSS4G et l'usage du logiciel de SIG ouvert. Ensuite, nous examinons la faS con dont un syst eme d'information communautaire conS cu avec le logiciel de SIG ouvert est utilis e avec succ es par une organisation environnementale a Milwaukee pour combattre la pauvret e urbaine. Notre recherche d emontre que le logiciel de SIG ouvert offre des possibilit es uniques pour faire progresser la recherche et la pratique du SIG pour la participation publique. Mots cl es : FOSS4G, logiciel de SIG ouvert, SIGPP, acc es au SIG