Part I - The quest for a natural social contract.- 1. Introduction.- 2. Sustainability transition: quest for a new social contract.- 3.Towards a natural social contract.- Part II - Theories and concepts.- 4. Conceptual background of Transformative Social-Ecological Innovation.- Part III -  A Research and Innovation Agenda.- 5. Analytical instruments for studying TSEI.- 6. Transition to a sustainable and healthy agri-food system.- 7. Governance of urban sustainability transitions.- Bibliography.