The introduction lays the foundation for the book and draws the link among the various chapters. It outlines the underlying principles and posture of the book: considering environment as a degraded common, promoting solidarity and respect among humans, acknowledging the diversity of human beings, co-constructing public policies, adopting South-North, gender-sensitive and indigenist visions. It explains the title of the book, based on the assumption that stakeholders must no longer simply be informed about the decisions that affect our social-ecological systems, but acquire the capacities to decide, act and adapt autonomously (what we call a "transformative participation"). It introduces the CoOPLAGE approach which is at the core of the book and provides definitions of key terms (stakeholders, engagement, modelling, etc.). It also summarizes the various chapters of the book.