More than 150 million people, mainly in developing countries, are affected by filarial nematode infections that cause debilitating and disfiguring diseases. Although transmission is restricted to the tropics and subtropics, imported infections sometimes occur in Europe and North America among immigrants and refugees from endemic countries, and rarely among long-term travelers. This article reviews the epidemiology of the most important human filarial nematodes, their current distribution, life cycles, clinical features, and disease burden. Diagnosis, treatment, and tools for prevention and control are discussed. Protective measures for travelers are summarized, and vulnerable groups and case numbers in North America identified.