This book introduces the companion modelling approach by presenting the stance that underpins it, the methods and tools used with stakeholders and the specific role of models during the process. It addresses the means to deal with the different levels of decision-making and to take into account the various power relationships. It proposes a methodology to assess the impact of the approach on the stakeholders involved in the process. The book includes 27 case studies and 7 teaching tools that describe the successful use of the approach in a variety of settings or teaching contexts. It is intended for researchers working on rural development or renewable resources management, as well as students and teachers.