This is the third and final article in a continuing education update series about arthropods. The first article explored identification of medically important arthropods. The second article dealt with how arthropods directly affect human health. This article highlights the role of arthropods as transmitters of disease agents. In mechanical transmission, pathogens may be transmitted to the host through the vector’s mouthparts or feet or be passively regurgitated during bloodfeeding. Biological transmission requires that pathogens go through a cycle of development or multiplication in the vector’s body before being transmitted to the host. In the United States, zoonoses are the most commonly diagnosed arthropodborne diseases, with tick-borne diseases particularly common.