Complementary to recognizing cities as contested sites of multi-level 'low-carbon politics', there is a need to account for the role cities (can) play locally in shaping civil society-driven sustainability innovations. This chapter takes up this perspective and explores how cities enable or constrain the emergence and formation of grassroots niches. It examines the implications for urban policy and governance and perspectives for a purposeful orientation of sustainability transitions. To start with, basic conditions for grassroots niche formation and their relation to urban contexts are deducted from research dealing with grassroots movements and their socio-technical transformation potential, and with spatially embedded social innovations. The chapter explores these conditions empirically through the study of a highly pertinent urban case – the evolving approach for 'village community' governance in Seoul – accounting for their articulation, identifying critical issues that arise from implementation, and deriving new insights for theory and practice.