Before the advent of molecular methods to identify non-culturable bacteria, symbiosis was thought to be a unusual character in animals, i.e., restricted to a few species, such as hydrothermal vent animals, termites and some luminous fish and squid. While these associations continue to provide ideal study subjects for the phenomenon of symbiosis, the technological advances of high-throughput sequencing have revealed a world far beyond our imagination. The data to date reveal that many, if not most, animals rely on partnerships with microbes for their health and survival. For example, work on vertebrates has demonstrated that the carriage of gut consortia is a shared, derived character in this subphylum of animals. This article highlights a few examples of research efforts in this field.