Bacteria, viruses, fungi, protozoa and prions are "invisible" beings that, however, develop decisive and paradoxical actions in our lives: at the same time that they make possible the existence of bread, cheeses, chocolate, fermented beverages and medicines, severely affect our health and are responsible for much of our diseases: 7 out of 10 deaths in industrializing countries are caused by microbes , and 2 out of 3 three children die worldwide from microbial diseases. Two-thirds of these deaths would be avoidable. It is therefore necessary to know these microscopic beings: to know what they consist of, what they differ in, what their origins, their effects and their consequences are, whether they are both their capacities to sicken and the beneficial effects they may entail. But it is necessary to know them in an appropriate way, and here lies the originality of this work: not only will you find a complete and explained list of each variety of microbes and the diseases and epidemics they cause, but they will be known in relation to the historical and cultural contexts in which they manifest themselves. Pablo Goldschmidt, PhD in molecular pharmacology at the Université Pierre et Marie Curie (Paris VI), Argentine biochemist specializing in pharmacokinetics, clinical pharmacology and antimicrobial pharmacology, answers precisely and clearly an itinerary of vital questions, among which, by way of illustration: How did these "invisible lives" appear? What are microbes? How do they feed? Why wouldn't there be oxygen without them? What microbes make humans sick? How do defensive systems mobilize to deal with their aggressions? What bacteria make the skin, mucous membranes, mouth, teeth, ears sick? What bacterial diseases are transmitted by fleas, lice, ticks and animals? How do bacteria contaminate newborns? What does disinfection, antisepsy, pasteurization and sterilization mean? What is sepsis? What are they and how did the viruses originate? How do they reproduce? What affect humans? What is the flu? What are colds and how do they get complicated? What diseases cause fungi to humans? What are the risks of stray animals, among many others. An extraordinary, complete, original work that can contribute to the best knowledge of these invisible beings.