Ticks of the Ixodidae family are important ectoparasites of humans and animals. Of the 80 or so species found in the United States, about 20 are of veterinary importance. Ticks are second only to mosquitoes as carriers of human pathogens. The ixodid (or hard) ticks are the most common and are represented by the genera Ixodes, Haemaphysalis, Boophilus, Rhipicephalus, Amblyomma, and Dermacentor. Accurate identification of the species of ixodid ticks within an area is a prerequisite to control and eradication. Therefore, veterinarians should have a working knowledge of the biology and identity of the more common mammalian-parasitizing ticks in the United States. In the United States, the argasid (or soft) ticks are less common than the ixodid (or hard) ticks. Argasids are represented by the genera Argas, Ornithodoros, and Otobius. Although the overall anatomy of the various species of argasids is similar, their functional approaches to feeding, reproduction, host finding and preference, tick-host behavior, tick relationship to their environment, and disease association vary among species. Accurate identification of the species of argasid ticks within an area is useful in their control.