All species of ticks (Acari: Ixodida) are grouped into three families: Argasidae (186 species), Ixodidae (692 species) and Nuttalliellidae (monotypic). Molecular markers have been developed and applied for tick studies along with conventional techniques. The origin of ticks is during the pre-mid Cretaceous period (with both the Argasidae and Ixodidae being established in the middle Cretaceous). Primeval hosts were probably reptiles or amphibians. The Argasidae contains two to five subfamilies according to authors but relationships among its members are far from resolved. The Ixodidae were formed by the basal Prostriata group (genus Ixodes subfamily Ixodinae) and the Metastriata group (all others genera). Conventional classifications considered Metastriata to be divided into Amblyomminae, Haemaphysalinae, Hyalomminae and Rhipicephalinae but evidences shows that part of Amblyomminae (species considered previously as "indigenous Australian Aponomma") are now members of the basal Metastriata subfamily Bothriocrotinae, and Hyalomminae are part of Rhipicephalinae. The former genus Boophilus is included as a subgenus within Rhipicephalus. The validity of tick names is discussed in relation to latest world list of ticks.