Sociotechnical transitions are important to address environmental problems. The present literature focuses on green options that break through and replace existing sociotechnical regimes. The project turns the analytical focus upside down, seeing the destabilisation and decline of existing regimes as the key to transitions. Regimes refer to the rules (knowledge base, belief system, mission, strategic orientation) shared by incumbent actors in an industry. Destabilisation results from increasing external pressures (economic, normative, regulatory) and eroding commitment of actors to regime rules. Research questions are: 1 To what degree have regimes in transport, energy and agriculture destabilised in the last 30 years, as a result of environmental pressures? 2 What kind of process is regime destabilisation and how should it be conceptualised for environmental problems? Which mechanisms are important and how do they interact? The project develops a theoretical perspective, combining insights from neo-institutional theory, STS, evolutionary economics. A phase-based pattern and three propositions are advanced. To investigate destabilisation, the project uses case studies as research strategy, which is appropriate for tracing complex processes such as changing beliefs and identities, fuzzy network boundaries, and many interacting (external) factors. Two PhD projects do four longitudinal case studies about destabilisation. Cases are selected with regard to the phase-based pattern and propositions. One case (decline of domestic coal) went though all phases. Another case (destabilisation of pig farming) has progressed far into the last phase. Coal in electricity and the car regime are less far in the phase-pattern, and probably less destabilised. The PI integrates findings from PhD projects, providing general answers to research questions. He also elaborates the inter-disciplinary perspective, and addresses the possibilities for sustainability transitions.