The presentation describes and analyzes the cooperation of the Sustainable Lifestyles Accelerator with Finnish and Spanish municipalities. The Sustainable Lifestyles Accelerator is a three-year program for upscaling sustainable lifestyles in Finland, Spain, Germany, Switzerland, Denmark, Mexico and India. It is based on the four steps of the transition cycle comprising problem analysis, vision development, experimenting and up-scaling. In the Sustainable Lifestyles Accelerator problem analysis means the calculation of the lifestyle carbon and material footprints of the participating households, vision development the co-creation of individual roadmaps towards 1.5-degree lifestyles by 2030 for each participating household, and experimenting a one-month phase where each participating household tries out several measures out of their roadmap. Up-scaling happens by extending the number of participating households per country from 5-10 in 2018 to 500 in 2019 and 10,000 in 2020. In addition, up-scaling means increasing the number of municipalities cooperating with the Sustainable Lifestyles Accelerator. The participating municipalities in 2018 were Porvoo in Finland and Sant Cugat del Vallès in Catalunya/Spain. Additional municipalities have joined in 2019. The Finnish city of Porvoo has committed itself to become carbon-neutral by 2030. Sustainable lifestyles are one of four focus points of the new city strategy adopted in 2018. In 2018, for example, eight households from Porvoo participated in the Sustainable Lifestyles Accelerator in 2018. In addition to the municipality, more than ten mostly local or regional companies participated by facilitating households’ experiments or implementation. The participating households were able to drop their average carbon and material footprints by 25 per cent during the experimental phase. In addition, the households provided plenty of feedback to the municipality on critical points for improving the ability of inhabitants to make their lifestyles more sustainable. The presentation concludes that a cooperation of municipalities of households like in the Sustainable Lifestyles Accelerator can provide municipalities crucial feedback on how to improve sustainability and how to approach their carbon-neutrality targets. Municipalities can facilitate the sustainability of their inhabitants’ lifestyles thus not only improving living conditions but also sustainability-oriented local business.