Currently, illegal wildlife trade is one of the greatest threats to biodiversity conservation. Understanding the causes that make some countries participate as wildlife suppliers or consumers is crucial to fight this criminal business in a more effective way. Using data provided by TRAFFIC, the wildlife monitoring network, the World Bank, the Agriculture Organization of the United Nations and the Migration Policy Institute, we identified 34 supplier countries (exporters) and 44 consumer countries (importers). Our objective was to determine which socio-economic factors could explain the geographical patterns of 42 vertebrate taxonomic groups that are involved in illegal wildlife trade. We used a hypothetico-deductive approach based on falsifiable hypothesis testing through observable predictions. We proposed that the main factors leading countries to become exporters could include economical needs (e.g. poverty), easy access to species on demand (e.g. lack of wildlife protection), and weak law enforcement (e.g. corruption). For importer countries, motivations were the increased consumption of luxury goods in emerging economies, weak law enforcement, demography (e.g. population size), and specific cultural reasons (i.e. Asian Traditional Medicine). Our hypotheses were tested using logistic regression to analyze the participation vs. non-participation of countries in illegal wildlife trade according to 17 predictor variables. We quantified the relative influence of different factors using variation partitioning analysis. Our results showed that a wide variety of factors potentially lead countries to participate in the illegal wildlife trade. Supplier countries are concentrated in Africa and Asia, and may be primarily motivated by economic needs and eased by weak law enforcement. There is a high overlap (63.2%) between the effects of both factors on wildlife export, but they still have individual explanatory capacity (27.7% and 9.1%, respectively). Demand countries are mostly found in Asia, followed by America and Europe. Their motivations could be mainly demography (39.2%), emerging economy (39.1%) and Asian Traditional Medicine (12.2%). The two former factors partially overlap with the Asian Traditional Medicine (>21%). We suggest that, in order to decrease the rates of illegal trade, crime prosecution and punishment should be complemented with international strategies for improving livelihoods in exporter countries. Better education, legal certainty and government transparency would also help minimizing illegal trade, by favouring a suitable social environment for law enforcement. Regarding consumer countries, we suggest a combination of environmental education and awareness, especially targeted at the wealthy middle class in emerging countries. In Asia, countries with deeply rooted traditional medicine could complement promoting environmental awareness with the search for sustainable and legal substitutes for wild-animal-origin ingredients.