Nature based solutions are amongst other practices that transition initiativeswork with when intervening in their place and change its fabric. Focusing on theactors establishing, driving and scaling these solutions in and across cities, we cometo evince that nature-based solutions have transformative social impact since theymediate new social relations and new social configurations contributing to socialinnovation in cities, and change nature perception and human-nature relations inurban contexts. We built from evidence in three city-regions that over the past yearsthey saw the proliferation of community-based and policy-based initiatives with theaim to improve sustainability, livability and the aspiration to foster inclusivity andsocial justice in their cities: the city of Dresden in Germany, the city of Genk inBelgium and the city-region of Stockholm in Sweden. We will elaborate on the differentways nature based solutions as practices of transition initiatives in cities getscaled and contribute to accelerating sustainability transitions in these city-regions.In line with this, we will draw cross-case lessons for urban planning on the tensionstransition initiatives that experiment with and institutionalize nature-based solutionsin their cities face when actively pursue acceleration strategies and pathways to scale.