**1. Introduction**

Giardiasis continues to be a significant parasitic disease in the world caused by the species of *Giardia* genus, particularly *Giardia intestinalis*, which affects humans and animals in a wide clinical spectrum, with zoonotic potential due to shared genotypes that can affect the same hosts. This protozoan disease occurs in developing as well as in industrialized countries, also affecting travelers. In recent years, multiple aspects in its epidemiology, but also and particularly in the long-term clinical consequences, have been highlighted. In this introductory chapter, a review on general aspects, based on recent experiences, is described.
