Trichomonads are anaerobic, flagellated protists belonging to the large phylum Parabasalia. In most cases, they exist as endosymbionts harmless comensals of invertebrates and vertebrates but several species are considered to be imported intestinal or urogenital parasites of humans and other animals. This paper presents current information on the taxonomy, morphology and biology of trichomonads. The characterization of invasiology followed by the description of virulence factors and pathogenic mechanisms of trichomonads is presented. The present paper also reviews diagnostic methods, treatment and prevention of trichomoniasis.