Ticks are among the most significant blood-sucking arthropods worldwide. They transmit various pathogens that can cause disease and death in people, domesticated animals, and wildlife. Ticks have several morphologic features and physiologic mechanisms that facilitate host selection, ingestion of vertebrate blood, mating, survival, and reproduction. Although the natural history of ticks varies considerably among species, these arthropods are well-adapted to survive in tropical, temperate, and even subarctic habitats. Key factors, including the reversion of agricultural lands to forests and a close association between people and ticks, have greatly increased the risk of tick bite and human disease.