The first decade after the fall of state socialism in Poland was characterized by moderate aspirations to reform or oppose the dominant (neoliberal) rhetoric by social movements in the country. In the last decade, a turn toward more informal grassroots activity has been observed by scholars, above all in the field of urban activism. This article looks into this recent development in urban activism and focuses especially on the hitherto neglected grassroots, noninstitutionalized, and nonformalized forms of activism that take place in Polish cities aimed at urban change. It will be argued that this form of urban activism developed as a reaction to professionalization and NGO-ization of social movements, defying the (until now) established forms of organizing collectively. The analysis is built on qualitative data gathered in 2014–2015, including 36 in-depth interviews with urban activists in informal initiatives and groups in different Polish cities.