Problems and methods of forest-biodiversity economic valuation iodiversity is a source of value in forests in that it participates directly in production (wood, hunting, various forest amenities, etc.), in regulating production (resilience in the face of hazards and uncertainties) and in adapting to changes that are often complex and abrupt. The many services rendered by ecosystems (see box ➊) often depend on biodiversity and thus enhance its value. A second aspect of its value lies in its non-market features, including culture, landscapes, philosophical and moral issues, that are not necessarily tied to "services". Finally, and this list is hardly complete, the existence value of the ecosystems and species making up biodiversity may be critical. Economic valuation of biodiversity is useful and perhaps indispensable for efficient forest management in that it makes possible, for example, comparisons of the costs and benefits between prior and modified situations (e.g. costs resulting from damage to biodiversity during forestry work). A monetary value placed on biodiversity is the means to provide decision-makers with quantitative data to determine the costs and benefits of programmes intended to conserve or modify biodiversity. This type of valuation raises a number of methodological problems and, to date, no efforts have been made to summarise the work on the topic and thus facilitate concrete case studies. That is why we wrote a book for public and private forest managers (Brahic et Terreaux, 2009) to assist them in selecting the method(s) best suited to the aspect of biodiversity requiring valuation. The book is based essentially on an analysis of international publications and through the various examples presented, it enables managers to put the inevitable difficulties into perspective and possibly find solutions for them. It is this work that we will present briefly here.