Multiple demographic or economic parameters contribute to the origin of emerging infections, for example: poverty, urbanization, climate change, conflicts and population migrations. All these factors are a challenge to assess the impact (present and future) of parasitic diseases on public health. The intestine is a major target of these infections; it is a nutrient-rich environment harbouring a complex and dynamic population of 100 trillion microbes: the microbiome. Most researches on the microbiome focus on bacteria, which share the gut ecosystem with a population of uni- and multi cellular eukaryotic organisms that may prey on them.  Our interest focuses on the families of eukaryotic microbes inhabiting the intestine, called “intestinal eukaryome”, that include fungi, protists and helminths. Knowledge on the reciprocal influence between the microbiome and the eukaryome, and on their combined impact on homeostasis and intestinal diseases is scanty and can be considered as an important emerging field. Furthermore, the factors that differentiate pathogenic eukaryotes from commensals are still unknown. This book presents an overview of the science presented and discussed in the First Eukaryome Congress held from October 16th to 18th, 2019 at the Pasteur Institute in Paris.