The arthropods (meaning: jointed feet) form a large group of organisms that includes the horseshoe crabs, crustacea, millipedes, centipedes, arachnids (spiders, scorpions, ticks, and mites), and the insects (flies and lice). This is a huge group of organisms, but fortunately, only a few are important as pathogens of cats and other animals. In this chapter, we will discuss some of the arachnids (ticks and mites) and some of the insects (lice, fleas, and flies) that cause or transmit diseases of cats. Another small group of the arthropods that is given a cursory coverage is the pentastomids.