Viruses exist at the borderline between the living and the non-living. Individual viruses probably outnumber all other systems in the world that contain nucleic acids. This talk illustrates the morphology of the different types of virus and the ways in which they invade host cells. The mechanism by which the viral genetic code is expressed is also described. Viruses constantly threaten the wellbeing of all complex organisms but they can also be extremely beneficial to them. Viruses transfer genes between different host species, add some of their code to their hosts’ DNA, and take some of the hosts’ code for themselves. In doing so, they can transform an evolutionary process. The production of the human placenta relies on a sequence of viral DNA that has been incorporated into the human genome. Signs of honeybee viral disease will be discussed along with activities in beekeeping that can reduce the problems created by viruses.