The 21st century city is a process, not an object; Henri Lefebvre describes urban form as a field of vectors representing encounter, assembly and simultaneity. Consistent with this notion, theories of urbanism such as guerilla urbanism and tactical urbanism propose spontaneous assemblies and small-scale interventions as a way of keeping up with the rapid growth of contemporary urban conditions. Whereas the ‘commons’ may be defined as inhabitable land that we share, my thesis takes interest in creating a ‘common’ in which we participate, seeking an intersection between tactical urbanism and guerrilla urbanism. My design proposes a kit of parts for urban furniture, allowing informal vendors to design their own marketplace; I also design a deployment system through which this kit of parts mediates between informal markets and various managers of public plazas around Toronto. I envision a process that spans reclaiming industrial off-cuts, furniture component fabrication, collaboration with informal vendors, negotiation of public space allocations with various Toronto Business Improvement Associations (BIAs), all together creating an informal market designed by diverse participants.