BACKGROUND Many plant species representing the hemi-parasitic genus Thesium play important roles in communities around the globe as evidenced by the numerous ethnobotanical and contemporary uses, and pharmacological activities. However, no attempt has been made to amalgamate and analyze all of the available information. A comprehensive survey is needed to highlight knowledge gaps, as well as to determine the economic importance and commercial potential of the genus. OBJECTIVE To provide a comprehensive report on the species diversity, geographical distribution, ethnobotany, contemporary uses, chemistry, pharmacology and toxicology of the genus Thesium, as well as to give insights into possible future research opportunities. METHODS Literature on the ethnobotany, contemporary uses, chemistry and pharmacology of Thesium was gathered from standard search engines (Google, Google Scholar, PubMed, SciFinder and Scopus) using the phrase Thesium, as well as generic synonyms. Additional information came from relevant books, theses, patents and label information from herbarium specimens in the National Herbarium in Pretoria, South Africa. Information on geographical distributions was compiled from regional floras, regional revisions, original species descriptions and databases (GBIF, IPNI, Plants of the World online and The Plant List). Scientific names and synonyms were validated through www.plantsoftheworldonline.org. RESULTS A total of 23 Thesium species, 17 from Africa and six from Asia, were found to have traditional and contemporary uses. Despite the near cosmopolitan distribution of the genus, no uses were recorded for Europe, Australia and North America. Thesium plants are most commonly used as medicines (18 species), functional foods and beverages (seven species), charms (six species) and crafts (three species), but also have several other minor uses. Charm uses were restricted to southern and East Africa, while several contemporary uses such as functional feeds and fodders, growth mediums and fertilizers and veterinary medicine were unique to Asia. Thesium chinense is by far the most utilized and versatile species with a total of 173 uses in nine use categories, followed by T. longifolium with 39 uses in six use categories. No specific trends were observed in the plant parts used. As a medicine Thesium is used to treat 137 ailments, predominantly reproductive and breast (22), respiratory tract (18), degenerative (11), digestive (11) and urinary (10) ailments. Chemical analyses are available for only eight species, with flavonoids, fatty acids and alkaloids as the main compounds. The potential influence of the host plants on the chemistry and pharmacology remains unexplored. The pharmacological activities of two species, T. chinense and T. viride, have been studied, while three other species are reported to be poisonous. Thesium chinense has analgesic, anti-inflammatory, anti-oxidation, chemopreventive, cytotoxic and other general therapeutic properties, and T. viride anti-bacterial activity. CONCLUSIONS This study has highlighted the ethnobotanical, contemporary and pharmacological importance of Thesium and informed possible future research opportunities. While ample information is available on the traditional uses of the richly diverse African Thesium species, the few Asian species dominate the literature on contemporary uses and pharmacology, while relevant literature on species in the rest of the world is altogether lacking. In light of the popularity of Asian species as ingredients in contemporary medicines and products, further research is needed into African species and their uses, including potential commercial uses. As an important medicinal hemi-parasite in both Africa and Asia, the identities of ethnobotanically relevant species and their phytochemistry, pharmacology and toxicology remain underexplored and require more research attention.