Knowledge of infectious diseases and their treatments is constantly evolving. New infectious agents are regularly discovered, due mainly to improvement of identification techniques, especially the development of molecular biology and mass spectrometry. While changes in the epidemiology of infectious diseases are not always predictable or readily understood, several factors regularly enter into consideration, such as not only the natural history of diseases and the impact of vaccinations, but also the excessive and irrational use of antibiotics. Antibiotic resistance is now recognized as one of the major challenges for humanity, especially since few new molecules have been put on the market in recent years. These molecules are reserved for serious infections caused by bacteria resistant to other antibiotics and should be prescribed only by infectious disease specialists trained in their use. Rationalization of antibiotic therapy is therefore one of the keys to reducing antibiotic resistance and the spread of resistant bacteria. In this guide, with regard to each clinical situation, the bacterial target(s) of antibiotic treatment, the preferred antibiotic choice, and the therapeutic alternatives will be specified. Comments on diagnosis and treatment of the infection will be added if necessary.