Introduction: Giardiasis, caused by Methods: The review was conducted in accordance with the PRISMA 2020 guidelines, using searches in the PubMed, LILACS, and SciELO databases for studies published between 2016 and March 2026. Results: A total of 114 studies involving humans, animals, and environmental samples were included. Only nine of these studies (7.9%) adopted a genuinely integrated One Health design that simultaneously evaluated two or more compartments, and assemblage-level molecular characterization was available for only 17 studies (14.9%); these proportions should be considered when interpreting the One Health framing and the molecular inferences of this review. Substantial methodological heterogeneity was observed across studies, encompassing different coproparasitological, immunological, and molecular methods. In humans, occurrence was higher in vulnerable populations and in areas with inadequate basic sanitation. Among animals, dogs, cats, cattle, and wildlife stood out as important hosts. In environmental samples, a high frequency of detection was recorded in water, sewage, and food. Molecularly, assemblages A and B predominated, both associated with zoonotic and anthroponotic transmission. Discussion: The findings reinforce the importance of integrated surveillance and One Health approaches for the control of giardiasis in Brazil.