Flea and tick infestations are common and elimination can be expensive and time consuming. Many advances in control of fleas can be directly linked to improved knowledge of the intricacies of flea host associations, reproduction, and survival in the premises. Understanding tick biology and ecology is far more difficult than with fleas, because North America can have up to 9 different tick species infesting cats and dogs compared to 1 primary flea species. Effective tick control is more difficult to achieve than effective flea control, because of the abundance of potential alternative hosts in the tick life cycle. Many effective host-targeted tick control agents exist, several of which also possess activity against adult or immature fleas and other parasites.