Gnotobiology is a field of study that focuses on the biology of germ-free animals or animals with known microbial environments. Synonyms for gnotobiology include microbiota research, germ-free animal research, and axenic animal research. Microbiota research deals specifically with the study of microbial communities in animals and their impact on health and disease. Germ-free animal research involves studying animals that have no microbiota and the effects of introducing different microorganisms to these animals. Axenic animal research relates to animals that are completely free of any microorganisms, including viruses and bacteria. All of these terms refer to the study of the interaction between microorganisms and animals in a controlled environment.