The parasitic flagella Giardia lamblia (also called as Giardia intestinalis or Giardia duodenalis) has emerged over the past decades as a major pathogen causing giardiasis. This species has two major forms in the life cycle: the trophozoite and the cyst, in which the cyst is the robust form and is very infectious and resistant in the environment. This causative agent has been associated with waterborne outbreaks. The infection can be spread directly from person to person by the Giardia infected person or indirectly from untreated water. Most people infections result from the use of water contaminated with Giardia cysts. Giadiasis is considered as a protozoan infection of gastroenteritis. An increasing number of waterborne Giardiasis outbreaks have been reported worldwide. This situation has become a major concern for safe drinking water for human consumption. In this review, relevant aspects of the biology and epidemiology of Giardiasis were discussed including the life cycle of Giardia, transmission and health effects of giardiasis, pathogenesis, method for detection of Giardia in water and measure to control Giardia.