Integrating environmental considerations into public contracts is now largely possible, enabling public purchasers to become real players in the fight against the ecological emergency and to influence the practices and behaviour of economic operators. However, major difficulties remain and, in practice, environmental aspects are often not implemented to any great extent. The aim of this book is to highlight and understand the practical obstacles preventing a genuine environmentalization of public procurement. Starting with the regulations in force in Canada, France, Italy, the Netherlands, Portugal and Switzerland, the research then focuses, through field surveys, on the various national obstacles preventing the development of green public procurement.