Toxocara is a parasitic helminth worm which continues to stimulate both public concern and scientific interest. "Toxocara canis" and "T.cati," the most studied species, are gastrointestinal parasites of dogs and cats and their eggs can contaminate the environment, thus exposing humans and other mammals and birds to infection. Many questions remain unanswered about the host-parasite relationship, its epidemiology and public health significance. Veterinarians and clinicians are interested in its importance as a zoonosis. The parasite's capacity to cause ocular disease is of concern to ophthalmologists, while its propensity to stimulate allergic manifestations is of interest to allergologists, dermatologists and respiratory medicine specialists. Furthermore "Toxocara" provides a unique model system to explore questions in parasite biology. This book provides a comprehensive review of Toxocara and the disease it causes known as toxocariasis.