Infectious diseases have accompanied human development from the earliest times and have often influenced it greatly. Although they were considered “an endangered species” in the second half of the 20th century, they continue to pose a serious threat to individual or public health. Diagnosis technique improvement, climate changes, increased population mobility and vaccine cover decrease are only some of the factors that have contributed lately to the occurrence and fast spreading of new pathogens or to the re-emerging of diseases already considered historical. Most of these infectious agents (Zika, Ebola, Chikungunya, MERS, SARS, new influenza viruses), for which there are few therapeutic resources, were the cause for regional or global epidemic outbreaks, which generated concern among healthcare professionals and often panic in the population, as well as significant economic losses. The international and medical communities joined their forces and got financially and logistically involved, sometimes paying with their own lives, in fighting these new threats. The fast understanding of the epidemiological process, pathogenesis and development of diagnosis and prevention methods has often helped limit the spread of emerging diseases and has laid the grounds for their future control.