Less than one percent of scientific literature on primates evaluate the effectiveness of interventions for the conservation of primates. That is the result of a new study compiled by a team of experts in 21 countries, led by researchers from the German Centre for Integrative Biodiversity Research (iDiv), Martin Luther University Halle-Wittenberg (MLU), Max Planck Institute for Evolutionary Anthropology (MPI-EVA) and the University of Cambridge. Despite great protection efforts, this is one of the main reasons for the dramatic decline of the populations of primate species. The study proposes several actions to improve the evidence base for the conservation of primates.