Ticks belonging to the family Ixodidae pass through 4 stages of development: egg, larva, nymph, and the sexually differentiated adult. The ticks discussed here are all 3-host ticks, meaning that they must locate and feed upon 3 different hosts in order to complete their life cycle. Animals that provide a bloodmeal are termed hosts. With the possible exception of the brown dog tick, none of these ticks is host-specific and, thus, will feed on a variety of vertebrates, including mammals, birds, and reptiles. Human are incidental hosts. Although important hosts, most bird species are not considered significant reservoirs of tick-borne pathogens and are more important for their ability to rapidly disperse ticks to new geographical areas. The manner in which ticks attempt to acquire hosts is called questing or host-seeking behavior and largely determines the type animal parasitized. Because of its importance as the vector of Lyme disease, human babesiosis, and HGA, the blacklegged tick will receive the greatest emphasis, but major differences in the biology, behavior, and ecology of the other tick species are noted.