In the field of the economics of outdoor recreation, special efforts have traditionally been made with regard to the evaluation of non-market benefits (i.e. the study of the “demand” side). Although this has unquestionably produced many very interesting results, from our point of view it has also led to the underestimation of another important aspect of economics i.e. the costs of outdoor recreation. Several publications have pointed out the multiple aspects of recreational costs (Loomis & Walsh 1997), including acquisition costs, operational costs, transaction costs, opportunity costs, congestion costs or even damage costs. For the reason outlined above, the costs that are neglected in market values (mostly congestion and damage costs) appear to have caught the attention of economists (Hanley et al. 2003). By comparison, other components of costs (acquisition, operational, transaction) have not received the attention they deserve and that they still lack sound economic analysis. Various reasons may be given: the data should be available a priori (in financial documents or contracts) or the subject should be relevant to engineering and not economics (because it refers to the installation of facilities which are generally designed and managed by technicians rather than social scientists). As a consequence, cost estimates frequently rely on ad hoc values (e.g. included in a local cost-benefit analysis) and little is known about their variability. In a world of scare resources, costs definitely do matter. By comparison, significant efforts have recently been made in sectors such as environmental conservation (see the survey of Naidoo et al. 2006, for instance). Where do we stand today with outdoor recreation?