Cestodes, or tapeworms, are flat, parasitic worms. Humans are infected by ingesting contaminated food or water, or by the accidental ingestion of infected invertebrate hosts. The parasite life cycles of all cestodes involve similar stages. Eggs are produced and hatch to form larvae, then the larvae transform into adult tapeworms. Infectious larvae develop in the parasite’s intermediate host(s), which are essential in the life cycle of all tapeworms. Adult forms inhabit the intestines of the parasite’s definitive host(s). Most gastrointestinal infections are minimally symptomatic, if at all, although high worm burdens are well known to cause symptomatic disease. Complications, including extraintestinal disease, are well described for those infections caused by Taenia solium and Echinococcus granulosus.