This Section of Epidemiology and Psychiatric Sciences regularly appears in each issue of the Journal to cover methodological aspects related to the design, conduct, reporting and interpretation of clinical and epidemiological studies. The aim of these Editorials is to help developing a more critical attitude towards research findings published in international literature, promoting original research projects with higher methodological standards, and implementing the most relevant results of research in every-day clinical practice. This article briefly presents the main characteristics of the World Health Organization (WHO) essential medicines list (EML), a register of minimum medicine needs for every health-care system. The idea behind the list is that the use of a limited number of well-known and cost-effective medicines may lead to improved long-term medicine supply, lower costs and better health care provision. The World Health Organization (WHO), established in 1948 after the Second World War, is a specialized agency of the United Nations serving as the directing and coordinating authority for international health matters and public health (World Health Organization, 2009). One of WHO's constitutional functions is to offer objective and reliable information and advice in the field of human health. The organization seeks through its publications to support national health strategies addressing the most pressing public health concerns of populations around the world. To respond to the needs of Member States at all levels of development, WHO publishes practical manuals, handbooks and training material, guidelines, analyses of health policies and lists of medicines to treat priority health care conditions (World Health Organization, 2009).The WHO essential medicines list (EML) is a register of minimum medicine needs for every health-care system (Bloom, 2011). The basic concept is that high priority drugs should be available as part of a functioning health system at all times for all people, guiding physicians to evidence-based and rational prescribing. The idea behind the list is that the use of a limited number of well-known and cost-effective medicines leads to improved long-term medicine supply, lower costs, better health care and more equitable and sustainable access to products (Hutchings et al. 2010).First published in 1977, the EML is revised every 2 years by a committee of experts from around the world in fields such as medicine, pharmacology, policy, regulation and health organizations (Hutchings et al. 2010). The expert committee updates the model list to reflect changes in global health concerns, pharmaceutical developments and patterns of drug resistance. The current version is the 17th WHO EML (updated in March 2011). The list is meant not to replace individual, national EML, but rather to be used as a guide to inform purchasing decisions in the context of national health agendas (Kishore & Herbstman, 2009