This work conducted to determine the prevalence, incidence and zoonosis of Giardia lamblia parasite between human and animal, which in contact directly and indirectly with showing the effect of the parasite on the public health. Also it identified the transmission of the parasite from human to animal and it s modes of transmission from the environment to human, the Nested PCR technique has been used to diagnose and identify zoonotic infection among cows and human. this book provide the clinical examination data of human and cow infected with Giardia, microscopical examination of Giardia, epidemiological study of Giardiasis in human and cows, zoonotic potential of Giardia between human and animal, the ability of Giardia transmission from human to animal and vice versa and determine the zoonotic gene responsible for zoonotic infction by nested PCR. This work is of benefit to the community and public health and researchers in the field of zoonotic diseases between human and animal, and also has a great economic importance and veterinary advantages for prevention and control transmission of Giardiasis.