Giardia and Giardiasis, Volume 106 in Advances in Parasitology series includes in the first part aspects of molecular and cellular biology of Giardia and the role of particular molecules or molecular groups in essential functions and/or trafficking in the parasite. These approaches are with the aim to explore how this parasite adapts to an ever-changing environment both within and outside of the host animal. Subsequently a comprehensive description of virulence factors secreted by Giardia, are reviewed on their cytotoxic mechanisms and roles in the pathophysiology of giardiasis, and also a description on the potential of these secreted molecules as targets for drugs is included. In the context of the immuno-pathogenesis of giardiasis a review on the data and information on innate and adaptive immunity to Giardia, is included as well as a discussion on how improved knowledge of immunity is advancing our understanding of the pathogenesis and clinical outcomes of giardiasis. The final part of this volume includes a review of the epidemiology of giardiasis in a veterinary context using molecular tools together with a discussion of the current status of the species and assemblages of Giardia, and issues surrounding the assignment of host specificity and the zoonotic potential using current molecular markers.