Current and future public health is characterized by the increase of chronic and degenerative diseases, corresponding to the worldwide ageing of the population. The increasing prevalence of these conditions together with the long incubation period of the chronic diseases and the restless technological innovations, offer new opportunities to develop strategies for early diagnosis. It is an important task of public health to critically assess the promises and the pitfalls of screening strategies. In this perspective, this MOOC will detail the background concepts of early diagnosis, the methods to assess the effectiveness and the efficiency of screening programs, the tools available of scaling up a local program, etc. In a second part of the course, current and future trends in screening in several conditions will be presented, including cancer, cardiovascular and metabolic disease, prenatal and neonatal conditions (including genetic screening), and communicable disease. By the end of this MOOC, students should be able to develop a public health perspective on screening and to actively participate to the evaluation of screening strategies. This MOOC has been prepared under the auspices of the Ecole romande de santé publique (www.ersp.ch) by Prof. Fred Paccaud, MD, MSc, Head of the Institute of Social and Preventive Medicine in Lausanne (www.iumsp.ch), in collaboration with Professor Antoine Flahault, MD, PhD, head of the Institute of Global Health, Geneva (www.igh.ch).