Zoonoses can be described as diseases caused by infectious agents that are transmissible between animals and humans (bidirectional), or transmissible from animals to humans (unidirectional), with terms such as reverse zoonosis or anthroponosis used to describe transmission in the opposite direction, i.e. from humans to animals. In this chapter we will cover organisms communicable between tilapia and humans, regardless of the direction of transmission, for organisms that are known to cause disease in people. The direction of transmission may not be known, or there may be spillover and spillback from one host to another, so that ‘who gave it to whom’ changes over time. Many zoonotic organisms cause disease in some host species or individuals, but not in others. Indeed, absence of recognizable signs or symptoms of disease is a major contributor to transmission of zoonotic organisms, especially foodborne ones, because apparently healthy people or fish harbouring pathogens are difficult to identify and segregate from food supply or food preparation activities. Some communicable entities, such as antimicrobial resistance genes, are not even organisms, but segments of genetic code that may be present as part of a communicable organism or in the environment.