Transport innovations like organised car sharing carry a potential to be environmentally more benign than private car ownership since they might fulfil a bridging function between car use and public-transport use. We conducted a qualitative study with 39 participants of two car-sharing organisations and found a change in their mobility-relevant decision-making context as the most important independent variable for giving up the own car and adopting car sharing. The results are embedded into a theoretical framework focusing on the importance of breaking through car-use routines prior to adoption, and their validity is tested in a subsequent quantitative study (in progress).