Members of the phylum Arthropoda are characterized by segmented bodies; paired, jointed appendages (legs and antennae); an exoskeleton; and bilateral symmetry. Included in this group are many creatures such as crustaceans, centipedes, millipedes, spiders, scorpions, ticks, mites, and insects. This chapter focuses on the classification, growth, and development of arthropods, providing key morphological characteristics of each arthropod group. Identification strategies for arthropods are presented, with discussion about traditional morphological identification techniques versus more recent molecular identification. The medical impact of arthropods, particularly insects and ticks, is provided, including both direct and indirect effects on human health. This chapter provides information concerning negative health impacts from arthropods such as bites, stings, allergic reactions, and disease transmission.