Giardiasis, caused by the parasite *Giardia*, is a significant public health issue, affecting millions of people globally, particularly in developing regions. The infection is characterized by diarrhea, abdominal cramps, bloating, weight loss, and malabsorption, with high prevalence and disease burden. Giardiasis also impacts veterinary health, affecting livestock and companion animals. The life cycle of *Giardia* is direct, with cysts being highly infectious and surviving for extended periods in various environments. Molecular typing tools have revolutionized the understanding of *Giardia* taxonomy, population genetics, and epidemiology, enabling better characterization of genotypes and subtypes. *Giardia duodenalis* is the most common species infecting humans and many mammals, with assemblages A and B having broad host specificity and zoonotic potential. Subgrouping within assemblage A and host-specific assemblages (C, D, E, F, and G) have been identified, reflecting host specificity and genetic diversity. Mixed infections are common, and the occurrence of unusual assemblages in humans suggests the need for comprehensive genetic characterizations. Population genetics studies indicate genetic recombination, challenging the traditional view of asexual reproduction. Zoonotic transmission is supported by epidemiological evidence, with beavers being a common vector in some regions. Further research is needed to understand the population structure and reproduction of *Giardia*, as well as to develop more discriminatory typing techniques to improve the molecular epidemiology of giardiasis.Giardiasis, caused by the parasite *Giardia*, is a significant public health issue, affecting millions of people globally, particularly in developing regions. The infection is characterized by diarrhea, abdominal cramps, bloating, weight loss, and malabsorption, with high prevalence and disease burden. Giardiasis also impacts veterinary health, affecting livestock and companion animals. The life cycle of *Giardia* is direct, with cysts being highly infectious and surviving for extended periods in various environments. Molecular typing tools have revolutionized the understanding of *Giardia* taxonomy, population genetics, and epidemiology, enabling better characterization of genotypes and subtypes. *Giardia duodenalis* is the most common species infecting humans and many mammals, with assemblages A and B having broad host specificity and zoonotic potential. Subgrouping within assemblage A and host-specific assemblages (C, D, E, F, and G) have been identified, reflecting host specificity and genetic diversity. Mixed infections are common, and the occurrence of unusual assemblages in humans suggests the need for comprehensive genetic characterizations. Population genetics studies indicate genetic recombination, challenging the traditional view of asexual reproduction. Zoonotic transmission is supported by epidemiological evidence, with beavers being a common vector in some regions. Further research is needed to understand the population structure and reproduction of *Giardia*, as well as to develop more discriminatory typing techniques to improve the molecular epidemiology of giardiasis.