The paper reviews various eco-feedback systems including carbon calculators and discusses how different disciplinary approaches conceptualise and explain anticipated impacts of these systems. The European collaborative research project e2democracy investigates how citizen participation combined with long-term CO2 monitoring and feedback can contribute to achieve local climate targets. Empirical results from local climate initiatives in Austria, Germany and Spain show positive effects in terms of learning about CO2 impacts, increased awareness, enhanced efforts and guidance as well as individual empowerment leading to slightly reduced CO2 emissions. The findings highlight that a combined approach integrating eco-feedback and (e )participation is promising to foster sustainability.