Virus, bacteria, archaea, parasites and yeast have evolved to be able to invade a wide range of hosts in a symbiotic or pathogenic manner. They are also able to modify the host biological processes (transcription, translation, transport, etc.), inhibit the host defenses, put in place new cellular compartments, or modify expression of the host genome. Moreover, these microorganisms can rapidly mutate, incorporate new genes into their genome or transfer genes into the host genome, playing a major role in the evolution of species. As we have seen with the current pandemic, it is important to continue to study these organisms using a multitude of approaches and techniques.