This article addresses two central—yet insufficiently explored—characteristics of some social movements: i.) abrupt and rapid social mobilizations leading to ii.) the construction of novel political processes and structures. The article takes a novel approach to these issues by combining social movement literature and the notion of free social spaces with transition studies, which focuses on large-scale socio-technical transitions. This theoretical integration highlights the co-evolution between free spaces and societal transitions, and it is based upon complexity-thinking, which is essential to deal (...) with non-linear dynamics. A key insight is that to enable bottom-up societal transitions, radical social movements need to proactively develop solid alternatives to existing societal structures, to be ready once a window of opportunity opens. This theoretical approach is empirically illustrated using the APPO-movement in Mexico in 2006. (shrink)